option to log just queries with some error - pgsql 7.1

Is there an option to log just queries that fail or output some warning in 
7.1? I'd like to use this to check for incompatibilities of various 
software with pgsql 7.1. Currently I get these errors:

ERROR:  parser: parse error at or near "."
ERROR:  parser: parse error at or near "."
ERROR:  parser: parse error at or near "."

etc

Would like to catch the real queries.

Btw: this is from phorum 3.2.11. It seems to work OK anyway, but still want 
to solve this.

Tomaz