Dimsim,
When that happens, just let it go back to IE4, then upgrade to IE5.0. Been there, done that!
Having said that, I vaguely recall from the distant past that on one occasion there was a version conflict on my system. I thought I had backed to IE4, tried to put IE5.0 on but *&^% machine thought it was still at 5.5 and wouldn't let 5.0 install. That may have precipitated my last reinstall
AA