Today I was able to download a new version of the OSU1 file from Microsoft. The offline upgrade went thru smooth and now the xbox start up just fine again!
The xbox now reporting version number 19041.5082 (rs_xbox_release_2010.201102-1500)
I have moved my Xbox out of the Xbox insider program...
I have the same problem and the same firmware version. I think that we have to wait until the OSU1 file version is up to date with this firmware version. In worst case senario, wait for the November update to be able to restore the Xbox