Any suggestions for resolving problems with nVision login performance?

Starting a few weeks ago, our users started experiencing a significant latency issue when logging into nVision.  Prior to this problem, it typically took 10-15 seconds from the time a user selected the nVision shortcut until the login window was displayed.  Now, that process takes approximately 1 1/2 to 2 minutes.  Once logged in, all aspects of nVision provide normal response times...it is just the initial login that is affected.  It doesn't matter whether we use a 2-tier or 3-tier connection.

We have been able to see server logs that indicate a significant increase in file transmission errors between the workstation and the server--it appears to take a lot more attempts to access certain files during the log-in process than it did before, but it is ultimately successful.  However, we have not been able to identify a reason why we have an increased error rate.  I do have a case open with Oracle Support on this as well, but we aren't making very rapid progress so I wondered whether other customers had run into this and had any suggestions.  Some users