The original error message is "Line too long".  If you don't see a line
that is too long, then you probably hit a Masm bug.

There is a long-standing bug in Masm 6.11 which generates error A2039
for no reason.  It's a bug in the parser that they cannot repro easily
(but of course, we can repro it just fine).  The workaround is to
insert comments and/or blank lines before the line where the parser
eventually chokes.

This is the reason for all the comments you see in source code that read

    ; Add unnecessary comment for MASM bug.

    ; This comment line works around a masm bug.

    ; This is a bogus comment because MASM is stupid and currently will
    ; not assemble this file without it.

    ; comment for masm 6.11 cause its a butthead

    ; comment to make masm happy

You can use one of the above, or make up one of your own.  Be creative!