It's likely that someone may come along and tell you to uninstall CS5 and reinstall. You could also try the following:
Close all CS5 apps and reboot. Rename the memorybalancercs5.xml file located at:
Win 7 x64: C:\Users\username\AppData\Roaming\Adobe\dynamiclinkmanager\2.0 (may be hidden)
Start PPro and set the preferences.
The file that you renamed will be recreated. If you encounter any problems, just rename the old file back to its original name.
I doubt that this "fix" will work, but it's worth a shot. The dynamic link manager controls how Adobe CS5 programs allocate and share RAM. Something must have gone awry during your install, as it makes no sense to me why PPro & AE would show different amounts of total RAM available.
Thanks I'll try that and see what happens, I hope that fix the problem
Thank you so much
You should be able to set Premiere Pro CS5 to reserve only 3GB for other programs; that is the minimum allowed for some reason.
From menu: edit/preferences/memory
Use your mouse to "slide" "RAM reserrved for other applications" setting to 3GB (slide all the way to the left)