This is because you did not understood the regular expressions at the fundamental level.

.*?
zero chars -> true -> after the current position is not (?!....) -> true -> return true

Use something like:

my $string = "ERROR blah license will expire";
if ($string =~ /^ERROR\b.+?(?:Error processing Cancel Execution|licens
+e will expire)\b/m) {
    print "NOT MATCHED\n";
}
else {
    print "MATCHED\n";
}
[download]

or:

if ($string =~ /^ERROR\b/m and $string !~ /\b(?:Error processing Cance
+l Execution|license will expire)\b/) {
    print "MATCHED\n";
}
else {
    print "NOT MATCHED\n";
}
[download]