Many errors are flagged by mh on a Reload, but some can be difficult to spot. Here is a list of common errors in Perl code which you can check for. Perl code is case-sensitive. Check your capitalisation. Unmatched parentheses, curly braces, quotes and delimiters.
Local variables lose their values outside their own section of code.
A global variable should not be declared inside a sub-routine. This is a vital point which applies only to mh, not to Perl generally. A new variable in a loop module is taken out of the loop if it is typed in the first column on the left of the screen.