JPG export glitch

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Hello
I've been working on a large series of graphics in vector format in which I
have been exporting directly from Corel Draw version 7.375 into JPG format
at 760 x 432 pixels. Everything was working fine for a few weeks. All of a
sudden CD decided to make glitchy exports. The graphics are schematic in
nature and have many 1 pixel thick parallel lines. The glitch is that the
exports show double thick lines in some places which looks absolutely
terrible. This occurs with all anti-aliasing options. I have a complete
set of the vector masters which were used to export the OK JPG's. If I now
export with one of the same "proven" masters the results are also now
glitchy. The graphics look fine in Draw and also in PhotoPaint. They only
appear glitchy when viewed in browsers. (MSIE 5.5 and Netscape 4.7) I
have tried all of the following to no avail.

replaced all Corel DLL's with fresh back up copy of DLL's
glitchy before and after JPG patch D7JPG(1).EXE
exported in CPT format and re-exported from PhotoPaint to JPG
uninstalled and re-installed Corel

I'm thinking of re-installing my OS but I just went through that pain a few
weeks ago. That's the only thing left I can think of trying but wonder if it
has any chance of helping.

TIA for any suggestions or recommendations
Steve