Please try updating at least one of your machines to Acrobat 9.5.1 and see if the issue persists.
Also, is Reader 10 installed on the same machine as one of these 9.3.1 installations? This configuration is not recommended at all.
Reader 10 was not installed on the same machine, no. Upgrading to 9.5.1 is not currently an option, nor will it become one for several months. We are in a corporate environment that is currently standardized on 9.3.1, and we have a number of applications that are dependent on that specific version. What other options can you offer that allow us to stick with Acrobat 9.3.1?