to bcsurf and studiotucker here is my advice (per yellow):

1. go back thru your files and sytematically remove all files uploaded by the module manager and the adv. cross sell mod.

this is a pain in the ***, but what i did was have three windows up, 1, a backup copy of my database prior to installing these mods *so that i could make sure i wasnt deleting anything that was an original file* 2, my current database, and 3, the zip file from the mods.... i compared the 3 and made sure i had everything deleted...

2. go to the phpmyadmin and delete anything related to either mod, including "module_version_tracker"....

3. re-install the module manager files, then go to zen cart admin and let it auto install, per the instructions. if it works, great... if it doesnt, follow the prior posts between yellow and i to re-create the .keep file

4. once module manager is working correctly, reinstall the x-sell mod, from the zip file yellow provided the link to a few days ago, in this thread... this is the most current version

i hope this helps?! it worked for me...