Inkscape EPS output unreadable

When I save an Inkscape drawing as an .eps file the resulting file is unreadable.

The local sign shop, using Adobe Illustrator, was unable to open any .eps file I produced with Inkscape.

When I save even something as simple as a single rectangle to .eps using Inkscape I find the following:
- Windows (Vista Home Premium, 32 bit) can't produce a preview
- Irfanview (with postscript.dll 3.98 installed) can't open the .eps file ("Decode error! Invalid EPS file (no EPS preview image available, try AFPL Ghostscript PlugIn)")
- Inkscape can't open the .eps file that Inkscape just created, either ("Failed to load the requested file" followed by file path). I do have ps2pdf.cmd and ps2pdf.sh in /inkscape/share.

I've tried rebooting, using the latest distribution (0.46) and the latest developer version (r21627, built Jun 19 2009), all with the same result.

I'd appreciate any help/insights you can offer.

Thanks,

Tim