Interesting...

Could you check out a few things for me?

1. As the user under which the script runs, execute "tnsping db_tns_name" where db_tns_name is the Oracle TNS name of the instance to which your script is attempting to connect
2. See if there is any additional error information in the Apache error log and if so, post it here
3. See if the file sqlnet.log was generated. If so, and it contains any additional information, please post it here

I am guessing this is an Oracle OCI problem, and not really a perl problem.

Update:

Is there any chance the instance to which you are trying to connect is an Oracle 9i instance, and the previous ones were 8i? Looking on Oracle Metalink (support site) I did see some problems with the 8i OCI talking to 9i instances.