unable to update wordpress plugin

Hi,

I'm using version 3.6.9 of wp e-commerce and it is telling me I need to update to 3.7.7. Everytime I try to upload the new version it just continues to unpack the file and never completes. So I manually replaced the files with the updated version. Now all the files are 3.7.7, but I am still getting the message telling me to upgrade.

Any ideas as to what's going on, or how I might fix this?

Thanks