connection error

i have installed apache-1.3.12+php4.0.0 with support to imap and mysql, i'm istalling imp+horde verision xxx.pre12, that works fine with a imap server but when i use a pop3 server i have the following error: the document contained no data, try again later or contact server's administrator, i did a backtrace in the page , now how can i see where is the error: #0 0x0 in ?? () #1 0x813e41a in php_if_count () #2 0x80ccc08 in zend_hash_minmax () #3 0x813f6eb in php_if_min () #4 0x813490c in execute () #5 0x80b860b in php_execute_script () #6 0x80d31e0 in apache_php_module_main () #7 0x80b4b2b in send_php () #8 0x80b4b6c in send_parsed_php () #9 0x8151073 in ap_invoke_handler () #10 0x8164a19 in ap_some_auth_required () #11 0x8164a7c in ap_process_request () #12 0x815c28e in ap_child_terminate () #13 0x815c43c in ap_child_terminate () #14 0x815c599 in ap_child_terminate () #15 0x815cbc6 in ap_child_terminate () #16 0x815d363 in main () #17 0x400fd1eb in __libc_start_main (main=0x815d00c <main>, argc=4, argv=0xbffffc94, init=0x8085a58 <_init>, fini=0x82323ec <_fini>, rtld_fini=0x4000a610 <_dl_fini>, stack_end=0xbffffc8c) at ../sysdeps/generic/libc-start.c:90