Performing calculations while on the window page while working on projects with more than 6 windows will display an error or access violation. Making changes to window parameters, saving the changes and selecting another tab such as the Site > Project tab prior to performing calculations will prevent this error from occurring.

EDIT: This error has been resolved in the latest version of EnergyGauge USA and no longer occurs if your software is up to date. It will still potentially occur if you have not yet updated beyond version 4.0.01.