This is most likely caused by your expressions being too complex or your data model having synthetic keys. Without seing the application it is a bit hard to give spot-on pointers, but below are some common guidance.
1. Make sure you have no synthetic keys in the data model (Ctrl + T)
2. If you have calculated dimensions, make sure they are not complex or even eliminate them by different solution
3. Disable all expressions. Enable them one bu one to determine if there is a specific expression that causes your problem.
4. Minimize usage of nested IF statements in your expressions.
5. If possible precalculate values in your script instead of in application objects, to decrease memory and CPU usage during runtime
For more detailed input, please attach a sample QVW so that the table object and your datat model can be evaluated. If the file is large, it will be enough to have it attached without any data (File > Reduce Data > Remove All Values)
