You're using patch 5.2. TGC put a new .X parser in 5.2 that freaking hates quad polys (something that some editors/exporters like DoGA loves.)
When you recompile the viewer code, you bring the bug with you. The first viewer was compiled under patch 5.1.
Three possible solutions: Delete DBP and re-install up to patch 5.1 only. Or, when you export your models make sure to triangulate them so that the multi-sided poly bug does not bite. Or, convert the .X file to the DBO format and get better speed, smaller file sizes, and more goodness as a perk.
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TAZ
You can find the DBO convertor in the Program Announcement forum.