webclass designer - 'unspecified error'

Getting an 'unspecified error' (thankyou, Bill) whenever I try to edit a new HTML template in the weblass designer, or to add an existing file to it.
I reckon it's because DW Ultradev is my default editor and Visual Studio doesn't want to play with the other kids but, in the absence of such high-end professional tools as FrontPage :eek: I can't test the theory... Anyone ever come across this before, and if so, any tips on how to get around it?
Figured it could be fun to create an IIS app but right now I'm ready to shout "Come back VBScript, all is forgiven!!"