Random quadrature encoder read errors from MDC2250

I'm having an intermittent issue that when I read the optical encoders from the MDC2250, it will occasionally send back an incorrect value, usually very far from the correct value. It appears that the internal value of the encoder has NOT been corrupted, but rather the mechanism the reads the encoder and/or transfers it to the host is having some issue. It is possible to read the encoder a second time and (usually) get the right value. Lately, it seems the error may be sending back values nearer to the correct one, so they are hard to trap.

In all other ways the controller seems to work fine as far as I can tell. The issue occurs on two different controllers I am using, that use different serial connections. I'm running in a Linux environment and using the RS-232 interface. The application is an autonomous field robot, so an odometer update error amounts to an unrecoverable mission failure.

Any thots, suggestions or help would be appreciated.

thanks