Show the full error message, which should include a file and line number. Then show us the lines in you code surrounding the line at which the error occurs at; making clear which is the actual line in error. If the rexpexp is a run-time regexp, i.e. the pattern comes partially from a variable, then explain where the variable gets its contents.

It may just be that you need to wrap that variable (if any) with \Q$variable\E.

Dave.