Just in case that the backslash in your single-quoted string gets interpolated, I would try forward slashes in the path:

my $CONNECT = 'Driver={MAS 90 4.0 ODBC Driver};Directory=S:/v440/MAS90
+';
[download]

... or escaped backslashes:

my $CONNECT = "Driver={MAS 90 4.0 ODBC Driver};Directory=S:\\v440\\MAS
+90";
[download]

In any case, I would print $CONNECT to debug whether it has the value you expect.