That's exactly the message I get when I don't use use Switch; Switch doesn't detect your code as being a switch statement, probably due to something elsewhere in the program. Source filters are fragile.

Remove bits of the program until perl -c script.pl no longer gives the error. The last bit of code you removed likely contains the code Switch has a problem with.

I know that some functions of Text::Balanced (used by many source filters including Switch) have problems with //, although I don't know if it'll result in this problem, though. split(//, $var, -1) can be replaced with $var =~ /(.)/sg.