I2C via Zippy2: connection timed out


I'm reading and writing registers of a I/O board in a loop.
There are 12 read/write operations and then 2 seconds of sleeping.

After a time of half an hour the communication breaks with
errno=110 Connection timed out

The problem seems not be caused by the I/O board, because after
restarting the program, the communiction doesn't work.
The communiction also doesn't work to another identical board.

The communication does not work again before I reboot the

Thanks for your help, Roland