virtualbox.org

VirtualBox: 2.1.4 (OSE)
Host: Ubuntu 9.04 (x86_64)
Guest: Fedora 11 (i686)

I recently installed VB GA 2.1.4 (OSE), that came with Ubuntu 9.04, on the Fedora 11 guest. Mouse integration seems to work fine. However, the auto-resize of guest display is greyed out for the VM. While installing the GA, I had to modify install.sh so that it could recognize the X version (1.6.1.901) and install the correct X drivers.

Any idea what could be wrong?

If it's grey, then the GA aren't installed properly, or the client isn't running to report it's status to the GUI. Fedora has, just like Ubuntu, the GA in their repo, albeit an older version than you're running probably. Why don't you install those?