AME can't encode 500x500 TIF image sequence

I'm using CS4 on Win 7 and trying ot export still image sequences.  The sequences are 500x500 TIFF files and import into Premiere Pro CS4 just fine.  I can scrub the timeline in PPro and they seem fine.

When I try to encode with AME, though, it always gives "Unknown Error" after getting about 1/4 of the way through the encode.  I've tried exporting different formats (AVI, WMV, etc) and have tried all sorts of different frame sizes, frame rates, bit rates, etc.  Always ends up with the same unspecified error.

Any ideas where to look?

Thanks in advance.

rgames