Line 192 is "$ACETmpltDir = ~s/$ACEEnvironment//g;".

That should be $ACETmpltDir =~ s/$ACEEnvironment//g;. Pay careful attention to the spacing around =~.

What you have at the moment is trying to apply the substitution to $_; then apply logical not (*) bitwise negation (~) to the numeric result of that:

$_='aaaaa'; print s[a][]g;;
5

$_='aaaaa'; print ~s[a][]g;;
18446744073709551610
[download]

and finally assign (=) that to $ACETmpltDir, but it falls at the first hurdle because $_ is undefined.

(*)Corrected. Thanks to AnomalousMonk