Unable to Upload Images into WP 3.0

Have you tried:

– deactivating all plugins to see if this resolves the problem? If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the default theme to rule out any theme-specific problems?

– resetting the plugins folder by FTP or phpMyAdmin? Sometimes, an apparently inactive plugin can still cause problems.

– increasing the available memory?
http://wordpress.org/extend/plugins/memory-bump/
http://wordpress.org/support/topic/253495#post-1017842

– reviewing http://wordpress.org/support/topic/411649