Hello Darrel,
thanks, it works now, but there are coming up some more problems:

When the timer makes 1 second tick, i call a subroutine which has several
serin2 and serout2 commands to read and set data from some other modules.
It seems to come to write and read errors (time out comes in the serin2 and serout2 commands).
Also reading and writing to the 12c bus with I2CREAD and I2CWRITE to
a display doesn't work any more correct.

I enabled tmr0, tmr1, rx1 and rx2

Regards,
Ralf