Hi, I'm here again :-)

I found .overview under ~/News/cache/nnimap:.....:INBOX.om_devel/

mv .overview overview.orig

M-x gnus-cache-generate-nov-databases

And now I can successfully select my folder

Now the .overview and overview.orig are different

Ciao
-- 
Walter Franzini, e-mail: walter@sys-net.it
SysNet, Via Digione 8, 27100 Pavia - Italy