Hi,
First run a self test, then run the internal alignment test, and upload the error log so the forum members can have a look at it.
My first guess is that the VarGain 50 and FixGain 50 errors from the self-alignment test probably indicate that there is an issue with the gain of the Variable gain amplifiers in the analog front-end.
To check this you should Inject an AC signal into the BNC inputs of channels 3 & 4 and measure the amplitude at the input of the ADC's from the same channels. Verifying these against the signal amplitudes of channels 1 & 2 should give you an idea if the variable gain amplifiers are suspect.
regards