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PHP Notice: Undefined index: SchemaVersion in /home/.sites/106/site3/web/mt/php/mt.php on line 180
PHP Notice: Undefined index: PluginSwitch in /home/.sites/106/site3/web/mt/php/mt.php on line 180

I got this message in my error_log of my http server. Thought it was a bug / problem in PHP
but in fact it are just normal messages about values and other settings not used.

changing the PHP.INI (error section) not loggin ALL messages anymore solved this issue quickly

The answer took some days (still one issue not answered by the sixapart team) but this one is solved