You may want to start with CGI::Session::Tutorial, for exemple you could let CGI::Session handle session IDs by itself (even in the parameter list). And maybe letting CGI::Session handle the whole thing through cookies would just work for you.

How do you "click" on myaccount.pl ? There's not link in the code you provided. And do you know what triggers the redirection, either an empty or an expired session?

All we see with your code here, is that you try to redirect from home.pl to welcome.pl (why just print the HTTP Location header field yourself when you could use CGI::redirect like in welcome.pl BTW?), and from welcome.pl to home.pl, that's neither helpful nor clear :). And your issue probably doesn't come from that bit of code.