I've just installed it and double checked that it's listed as installed, Microsoft .NET CF 2.0, but still the same error message unfortunately

Thanks for the suggestion though.
EDIT: Hmm, for some reason the file OpenNETCF.Windows.Forms.dll wasn't copied when all the other files came across from the laptop to the PPC. Not sure why that happened. It's opened up and all working fine, silly me! :D