in reply to Backward compatibility of code problem
Most likely, you will need to re-install the CPAN modules that are required by your application, after completely destroying (that is to say, renaming!) the existing CPAN library subdirectory that your application requires.
When you undertake the apparently-simple task of “installing a CPAN package,” depending on the package, considerable magickal version-specific voodoo (ommmmm....) might occur! ... all of which, properly, should be none of your concern. (You waved the black rod with the rusty star on the end, just like the instructions told you to do, and a crystal bridge now spans the fissure, and that should be the end of it.) Now that your host has switched Perls on you, these processes must be repeated, as though they had never been done before ... as, effectively, they have not. You need for all of the CPAN installations to start over from scratch, considering only the new environment and assuming that no packages (other than those provided by the new environment ...) exist. If you can be sure of that, all should be well.
P.S.: If the hosting company in question happens to be 1&1 Internet, and you discover that they have now set the memory ulimit too small to run cpan anymore, remember cpanm.