Since you don't actually mention what command you're using, I'll give you an example, you need to make sure you're entering it correcctly.
Say I wanted to uninstall "e-smith-portforwarding-0.2.0-02.rpm", I would type rpm -e e-smith-portforwarding-0.2.0-02 (note the dropping of the .rpm). Is this what you're doing?