Plugin expects that text data in DB stored as UTF-8 strings.
If you are using different database encoding ( win-1252, iso-8859-1, etc. ) it may cause error during xml processing for umlauts.
You can check collation of database and events_rec table.
If issue still occurs - please provide a link to page where it can be checked ( you can send me a PM )
As for debug mode issue - problem confirmed and will be fixed in few days.