I have a rooted Desire, running the latest 2.2 and this problem seems to appear and disappear periodically every few months and I've tried everything to find the root of the problem, and by everything I mean the following:
cleared gmail cache
cleared gmail data
cleared gmail data & cache at the same time (the daredevil that I am)
removed the second google account and re-added it
uninstalled gmail market updates
tried re-installing gmail market updates, but they somehow wouldn't so eventually I had to...
adb into the device and rm the gmail .apk and .odex
re-install gmail freshly from market
This appears to have fixed it, but it only works if you have root, unfortunately.
Take care, IceBone (a somewhat happier camper)