I am running version 3.7.1-pro(Linux) hosted on Ubuntu 10-4 (32 bit) What is the host O/S you are using? Are you running on a virtual machine and how is it configured? Initially I got these error messages frequently, but this was reduced significantly when I altered my setup. I was running my jasper server sandbox on a Virtual machine using the Oracle Virtual Machine. After I changed the configuration from 4CPUs/4GB of memory to 2CPUs/4GB of memory, the number of times I got the error message dropped, however, I still get the error messages from time to time. At the moment I still get the error messages if I leave Excel open for a while (3 mins+) and then attempt to continue my analysis, or sometimes when I attempt to expand/collapse a row or filter component or just add a new filter to my workbook. There isn't an apparent pattern to this yet, but I will still keep at it.