This problem occured while running Package Manager on RH5.2 on an Alpha. I have also found this to happen on RH5.0 on Intel. Anyway, here's the deal: Whenever I try to use the 'uninstall' button in RH's package manager (X control panel) it in fact does start a copy of rpm, but it goes zombie on me in about a second. Similar problems have occured while using the 'install' button.
(I was using rpm ver 2.5.5 when these problems arose)
This is not an rpm bug. Make sure you have the latest errata update for glint installed. Please reopen this bug if your problems persist.