HERE IS THE SOLUTION
its by Gezelligheid(not me.. but it worked for me thanks buddy )
For those on N900 still not coming past the FB-authorization screen. This worked for me and it is a great app!
Delete Kasvopus__0.9.3 with the app.man.

Open http://www.substanceofcode.com/downl....9.2_armel.deb in MicroB.
On prompt click 'open with app.manager'.

When installed, open the app and just authorize Kasvopus to use FB. and make sure "Keep me logged in'' is ticked.
Have a look around at the previous version, because it's already really nice.
And then just download and install version 0.9.3. right over it, in the same way as mentioned above.


It's the best app on N900, by far! Really appreciate it. Thanks so much.
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i was getting exactly the same error and above solution worked for me...
actually its the first comment on the "kasvopus" download page...