unfortunately it wasn´t the latest version... it was (by mistake i started an old instance instead of my new installation. but anyway...

the last entry in server log was " |CRITICAL|ParamParser | | Assertion "positionHint <= m_MyPiece.m_paramSize" failed at common/parameter/parameterparser.cpp:252;"

as far as google told me, it can be an exploit in older TS3 versions.

i hope my update to the latest version (now for real ) solved the problem