Problem with diagnostics of step7

[rulomi]

Hi, I use the CPU 417-4H from Siemens with the Wincc interface. To the system are connected analog inputs SM 331 that are not connected to anything (just a resistor). Even that they are connected only to a resistor and they are in a closed cabinet with no vibration they are giving from time to time a wire break message. The wire break is not consistent with anything and is coming randomly just for about 20 msec each time. Did any buddy have this kind of problem? does anyone knows how to solve it?