I have this issue, I installed selenium RC, ActivePerl and PerlExpress 2.5, I ran some scripts, recorded some other with IDE and after modified with RC re ran as RC scrips, everything perfect.
After a month i try to run a selenium RC script that was working fine using perl express and got tons of error popups with numbers, at the end I got this
NOTE: to use the Run/Continue command in Perl Express you must have a Perl interpreter installed.Also, a correct path to perl.exe must be specified (View|Options - Perl).

If i go to perl expres / view / Options / perl I found the path to perl empty, when i setup i got this error

Access violation at address 00496C08 in module 'Perl Express.exe'.Read of address 00000000.

NOTE: I'm using Windows Vista :-( and perl because it is what we use on my company