The most likely cause is that Mailman was configured and installed incorrectly. Please read the INSTALL instructions again, paying close attention to the --with-cgi-gid configure option. This entry is being stored in your syslog:
Failure to exec script. WANTED gid %ld, GOT gid %ld. (Reconfigure to take %ld?) PYTHONPATH= %s -S Mailman cgi-wrapper (listinfo) listinfo driver %s 8p % @_ ʅڅ *:JZjz t ( ܄ Q d = d H < W I 1 W | . R | $) < g h s * t B u Y v q w x z { . 4 9 @ F E ~ P ( 7 , / E Z s k4 * A X r ] + / 2 2 L 3 g 4 5 7 @ C D 4 . 5 D 6 X 7 m 8 9 < = > ? A B & C H E _ F G H I J K L M . N E O ] P r Q R V X Y Z k 5 L e | 1 K e x $ > = = = D > D G D I D P & D Q 3 D R F D ] K D ^ [ D _ h D ` u D a D b D c D d D e D f D g D h D i D j D k D l D m / D o 4 D q J D r U $ > = = = @ = D U $ U $ z y 4 y D z D { D | D } D ( D - $ z y 4 y G @ y Z @ { - $ - i $ { D D " D 7 D 9 D I D S D x D D D D D D D D D $ D ; D F D X D b D i D D D D D D D D D i $ { @ @ @ @ . $ d 5 d 8= d 8H < W I 1 W | . R | d 8 d 8K d 8H < W I 1 W | . R | $) < ~ P / E Z s k4 r ] 1 K [ m { ! $ & 8 % % % D & D * D + D 3 ' D 4 . D 5 5 D 7 = D 8 P D 9 t D : { $ & 8 % % % @ % @ ' ( { $ { d common.c /usr/ports/mail/mailman/work/mailman-2.0beta5/src/ ./common.c gcc2_compiled. int:t(0,1)=r(0,1);0020000000000;0017777777777; char:t(0,2)=r(0,2);0;127; long int:t(0,3)=r(0,1);0020000000000;0017777777777; unsigned int:t(0,4)=r(0,1);0000000000000;0037777777777; long unsigned int:t(0,5)=r(0,1);0000000000000;0037777777777; long long int:t(0,6)=r(0,1);01000000000000000000000;0777777777777777777777; long long unsigned int:t(0,7)=r(0,1);0000000000000;01777777777777777777777; short int:t(0,8)=r(0,8);-32768;32767; short unsigned int:t(0,9)=r(0,9);0;65535; signed char:t(0,10)=r(0,10);-128;127; unsigned char:t(0,11)=r(0,11);0;255; float:t(0,12)=r(0,1);4;0; double:t(0,13)=r(0,1);8;0; long double:t(0,14)=r(0,1);12;0; complex int:t(0,15)=s8real:(0,1),0,32;imag:(0,1),32,32;; complex float:t(0,16)=r(0,16);4;0; complex double:t(0,17)=r(0,17);8;0; complex long double:t(0,18)=r(0,18);12;0; void:t(0,19)=(0,19) common.h /usr/include/stdlib.h /usr/include/sys/cdefs.h /usr/include/machine/ansi.h __int64_t:t(4,1)=(0,6) __uint64_t:t(4,2)=(0,7) __int8_t:t(4,3)=(0,10) __uint8_t:t(4,4)=(0,11) __int16_t:t(4,5)=(0,8) __uint16_t:t(4,6)=(0,9) __int32_t:t(4,7)=(0,1) __uint32_t:t(4,8)=(0,4) __intptr_t:t(4,9)=(0,1) __uintptr_t:t(4,10)=(0,4) rune_t:t(2,1)=(0,1) size_t:t(2,2)=(0,4) wchar_t:t(2,3)=(0,1) div_t:t(2,4)=(2,5)=s8quot:(0,1),0,32;rem:(0,1),32,32;; ldiv_t:t(2,6)=(2,7)=s8quot:(0,3),0,32;rem:(0,3),32,32;; /usr/include/stdarg.h va_list:t(5,1)=(5,2)=*(0,2) /usr/include/syslog.h /usr/include/stdio.h fpos_t:t(7,1)=(4,1) __sbuf:T(7,2)=s8_base:(7,3)=*(0,11),0,32;_size:(0,1),32,32;; __sFILE:T(7,4)=s88_p:(7,3),0,32;_r:(0,1),32,32;_w:(0,1),64,32;_flags:(0,8),96,16;_file:(0,8),112,16;_bf:(7,2),128,64;_lbfsize:(0,1),192,32;_cookie:(7,5)=*(0,19),224,32;_close:(7,6)=*(7,7)=f(0,1),256,32;_read:(7,8)=*(7,9)=f(0,1),288,32;_seek:(7,10)=*(7,11)=f(7,1),320,32;_write:(7,12)=*(7,13)=f(0,1),352,32;_ub:(7,2),384,64;_up:(7,3),448,32;_ur:(0,1),480,32;_ubuf:(7,14)=ar(0,1);0;2;(0,11),512,24;_nbuf:(7,15)=ar(0,1);0;0;(0,11),536,8;_lb:(7,2),544,64;_blksize:(0,1),608,32;_offset:(7,1),640,64;; FILE:t(7,16)=(7,4) /usr/include/string.h /usr/include/errno.h /usr/include/sys/types.h /usr/include/sys/inttypes.h int8_t:t(11,1)=(4,3) int16_t:t(11,2)=(4,5) int32_t:t(11,3)=(4,7) int64_t:t(11,4)=(4,1) uint8_t:t(11,5)=(4,4) uint16_t:t(11,6)=(4,6) uint32_t:t(11,7)=(4,8) uint64_t:t(11,8)=(4,2) intptr_t:t(11,9)=(4,9) uintptr_t:t(11,10)=(4,10) /usr/include/machine/types.h _physadr:T(12,1)=s4r:(12,2)=ar(0,1);0;0;(0,1),0,32;; physadr:t(12,3)=(12,4)=*(12,1) label_t:T(12,5)=s24val:(12,6)=ar(0,1);0;5;(0,1),0,192;; label_t:t(12,7)=(12,5) vm_offset_t:t(12,8)=(0,4) vm_ooffset_t:t(12,9)=(4,1) vm_pindex_t:t(12,10)=(0,4) vm_size_t:t(12,11)=(0,4) register_t:t(12,12)=(4,7) intrmask_t:t(12,13)=(4,8) inthand2_t:t(12,14)=(12,15)=f(0,19) ointhand2_t:t(12,16)=(12,17)=f(0,19) u_char:t(10,1)=(0,11) u_short:t(10,2)=(0,9) u_int:t(10,3)=(0,4) u_long:t(10,4)=(0,5) ushort:t(10,5)=(0,9) uint:t(10,6)=(0,4) u_int8_t:t(10,7)=(4,4) u_int16_t:t(10,8)=(4,6) u_int32_t:t(10,9)=(4,8) u_int64_t:t(10,10)=(4,2) u_quad_t:t(10,11)=(10,10) quad_t:t(10,12)=(11,4) qaddr_t:t(10,13)=(10,14)=*(10,12) caddr_t:t(10,15)=(5,2) c_caddr_t:t(10,16)=(10,17)=*(0,2) v_caddr_t:t(10,18)=(10,19)=*(0,2) daddr_t:t(10,20)=(11,3) u_daddr_t:t(10,21)=(10,9) fixpt_t:t(10,22)=(10,9) gid_t:t(10,23)=(10,9) ino_t:t(10,24)=(10,9) key_t:t(10,25)=(0,3) mode_t:t(10,26)=(10,8) nlink_t:t(10,27)=(10,8) off_t:t(10,28)=(4,1) pid_t:t(10,29)=(0,1) rlim_t:t(10,30)=(10,12) segsz_t:t(10,31)=(11,3) swblk_t:t(10,32)=(11,3) ufs_daddr_t:t(10,33)=(11,3) uid_t:t(10,34)=(10,9) dev_t:t(10,35)=(10,9) /usr/include/machine/endian.h clock_t:t(10,36)=(0,5) clockid_t:t(10,37)=(0,1) ssize_t:t(10,38)=(0,1) time_t:t(10,39)=(0,3) timer_t:t(10,40)=(0,1) fd_mask:t(10,41)=(0,5) fd_set:T(10,42)=s128fds_bits:(10,43)=ar(0,1);0;31;(10,41),0,1024;; fd_set:t(10,44)=(10,42) /usr/include/unistd.h /usr/include/sys/unistd.h /usr/include/sys/_posix.h scriptdir:G(10,17) moduledir:G(10,17) python:G(5,2) running_as_cgi:G(0,1) fatal:F(0,19) ident:p(10,17) exitcode:p(0,1) format:p(5,2) ident:r(10,17) log_entry:(0,20)=ar(0,1);0;1023;(0,2) check_caller:F(0,19) parentgid:p(10,23) parentgid:r(10,23) mygid:r(10,23) run_script:F(0,1) script:p(10,17) argc:p(0,1) argv:p(0,21)=*(5,2) env:p(0,21) argv:p(0,21) envstr:(0,22)=ar(0,1);0;11;(0,2) envlen:(0,1) envcnt:r(0,1) i:r(0,1) j:r(0,1) status:r(0,1) newenv:(0,21) newargv:(0,21) ./vsnprintf.c ./cgi-wrapper.c logident:G(10,17) script:G(5,2) parentgid:G(10,23) main:F(0,1) argv:p(0,20)=*(5,2) env:p(0,20) argv:p(0,20) env:r(0,20) fake_argv:(0,21)=ar(0,1);0;2;(5,2) [ASM_FILE_END]GCC: (c) 2.95.2 19991024 (release) [ASM_FILE_END]GCC: (c) 2.95.2 19991024 (release) [ASM_FILE_END]GCC: (c) 2.95.2 19991024 (release) [ASM_FILE_END]GCC: (c) 2.95.2 19991024 (release) [ASM_FILE_END]GCC: (c) 2.95.2 19991024 (release) [ASM_FILE_END]GCC: (c) 2.95.2 19991024 (release) 01.01 01.01 01.01 01.01 01.01 01.01 .symtab .strtab .shstrtab .interp .note.ABI-tag .hash .dynsym .dynstr .rel.bss .rel.plt .init .plt .text .fini .rodata .data .ctors .dtors .got .dynamic .bss .stab .stabstr .comment .note # 1 (( 7 ? G ܄ P Y tt _ 0 d j p x xx $ ~ T ` V2 , , 3 x 3 8 p 8= ( ܄ t x , $ + 2 1 9 ą B Q Z a ԅ i p w k t * $ h 4 U x D TY d: t + 8{ 0 * 7 - D J p Q X n s [ x common.c vsnprintf.c cgi-wrapper.c strcpy getgid printf strerror running_as_cgi _DYNAMIC _etext getegid execve malloc vsnprintf _init environ fprintf script strcat parentgid run_script end python setregid fatal __progname _start __error openlog closelog strncmp __sF logident scriptdir __bss_start main syslog check_caller _fini atexit _edata _GLOBAL_OFFSET_TABLE_ _end exit moduledir