In the latest version of the script (version 1.0, released in 2010), line 281 is just an 'if' test that is checking to see the strandedness of the match. It is possible that the format of Infernal has changed and what is being evaluated isn't numeric. That will cause Perl to die, but with a specific message telling you what happened (at least in recent versions of Perl, I can't conveniently test this with older releases right now).
Unfortunately, the script saves the Infernal results in the tmp directory with just the process id for the name, so debugging is not straightforward. You could change line 260 by replacing the /tmp/$$.res to infernal.$$.out and change line 262 from return /tmp/$$.res to return infernal.$$.out and that should give you a results file in the working directory you can inspect. You'd then want to see if the results match the regex in the Infernal parsing sub of that script. There could also be an issue with your particular results, so posting a couple of lines of the Infernal output might help us see what the issue is.
If the above advice is not clear then you may want to start by letting us know the script and Perl version you are using. Also, please let us know if you solve the issue from the help list so there is no duplication of efforts.