I do not know of any common failure modes associated with the 6025E. However, it is possible to damage these devices over time. Have you tried to run the E-Series self diagnostics(http://www.ni.com/support/selftest/)? It is extremely helpful in finding hardware problems.
I have noticed in the past that if you are not using the correct grounding mode, the signals may float around and do crazy things. Make sure you use DIFF or NRSE for grounded signals and RSE for floating signals in general. You can measure floating signals with DIFF and NRSE, buy you need to add bias resistors.
I do not know what you mean by "trashing the signals passing through the card", because the card is not designed to pass signals and it does not have an signal conditioning featu
res. Are you using any signal conditioning hardware? If so is it configured in MAX.
I hope this helps out.
Joshua
