As database is too big to be attached, I can provide you a link to it via pm (sending right now).
A little too big to attach at 800+MB...
Downloaded and restored to my sandbox - all 3.3million rows..
The download per your email was from before your 1.5.26 upgrade (and obviously pre utf-8 conversion).
A quick look shows forum tables looking like: (boards)
Здесь хранятся только удаленные сообщения и темы!...
and cpg tables looking like: (categories)
ÑдеÑÑŒ можно размеÑтить фотÐ...
Your cpg tables all restored with collation of latin1_sweedish_ci... Your forum tables are mostly utf8_general_ci with a few using latin1_sweedish_ci.
If this replicates your database successfully - I think the approach is to find a way to extract the cpg data, redefine and reload in a format matching smf - with appropriate settings to read it all.
I can't picture what in 1.5.26 would have changed the behavior - as the conflicting types were obviously there... unless you had some mod in the previous release?? You said 1.5.25 was your previous release?? - the normal release numbers are even (1.5.24, 1.5.26) If you pulled a specific SVN level after 1.5.24 - let me know which one and if that was to address a specific issue you were having...
As a side note... 2.9 million of your rows are in the `parnat_forum_log_errors` table... I would suggest emptying/truncating that table - unless you really have a need for that information... Will leave you with a much more manageable database...
The messages in there are all readable from character set perspective
8: Undefined variable: screen_res<br />Файл: /home...