If there is a problem such as a TT syntax error, it generally shows up as a an ugly server failure page. If you check the Apache error logs, you will probably find some solid clues about the reason for the failure. For example, in the following example the error message identifies the file in which the problem occurred as well as the relevant line numbers:

Example error message in Apache error logs. 

bash# grep "template error" /var/log/apache2/error_log
[Tue Dec 06 02:12:09 2011] [warn] [client] egweb: template error:
  file error - parse error - opac/parts/record/summary.tt2 line 112-121:
  unexpected token (!=)\n  [% last_cn = 0;\n        FOR copy_info IN
  ctx.copies;\n            callnum = copy_info.call_number_label;\n