i would love a fix for this too... getting the same error...
thanks for your great work guys ... i really appreciate it ...
I was able to successfully install the Grails Support extension this morning using the extensions tab. Thank you for resolving this.
I just verified the extension install for the "Grails Support" and it works fine in my tests.
If you get the above error message please try again after an hour as this might be caused by a running build which temporally updates the update site location.
I was able to install it just at this moment at (50%) now. After 3 gruelling days. I decided to uninstall everything again and reinstalled it in another drive instead of C:\. (I tried making the C:\ attribute read only to false and modifying the read only registry but did not do it). If anyone facing the same prob, try installing STS or eclipse in another drive other than C. thanks