If yo do a databse backup over the build in backup tool you run in trouble while importing it again. The export tool put every ~30kb a ; and a single line in the export like this (w3t_Last):
INSERT INTO w3t_Last VALUES ('UBB30','686','1105784265');
INSERT INTO w3t_Last VALUES ('UBB28','139','1118695875');
If you like to import this export with phpmyAdamin you must first edit the export and clean out the space lines or the import will fail.