theres no data to be lost really unless you already have manually put maps on there...i did that witd it worked ... i had the same error msg you guys had too
ignore the instructions regarding symbian ovi maps. just download the zip files for the countries you need, and then extract them somewhere and copy them in the MyDocs/cities/diskcache folder.
What I don't get is why Nokia make it so complicated in the first place.
Why don't they just have an option in Ovi Maps itself to just "pre-cache region" and show a list of areas you can download - right there on your phone. Even smartphones should do that, bearing in mind they are telling us the N900 is more a computer than a phone, why should we need to use ANOTHER computer to do it? (although the unofficial method we could do directly on the N900 I suppose)