The way I used to upgrade to 2.0.6 from 2.05 is backup all database from phpMyAdmin control panel and output the .sql file. Wiped out the old stuffs and installed new version then use SQL to restore the database. Because it works fine for me last time(upgraded to 2.0.5).

But this time every thing seems worked fine except the 'Site Preference>Mail setup' after I restore the database from the backup file (.sql).

It displayed blank page when I click Mail setup. So I tried to find out why, then I found the number of users in database (_users)seems to be the key.

I tried restored only 372 users (after many trials, by using SQL and .sql)to database and it shows blank page, but it appears normal again after I delete 1 user from database ramdonly (from time to time). To be sure it was not caused by the process of restoring, so I registered a new user from the site, then it ('Mail setup') comes up blank page again when I click the 'mail setup', but resume normal after I deleted any one of the users from database, it seem like 371 is the threshole... anybody have a clue how to fix it? or where can I do more research?
Tks

anybody has some clues yet?

I've got the same problem so any advice would be helpful.

I guess nobody has figured out how to deal with this? I wonder how come it happens only to few of us?