An exec error may appear when an executable file with an EXE extension encounters a problem or has corrupt data that prevents it from loading and running. Examples of Exec error messages are "Fatal Exec. Engine Error," "Compile error in hidden module: AutoExec" and "Excel has performed an error in module excel.exe and will be closed." Exec errors occur when saving a program with an EXE file name extension. They are caused by improperly installing or uninstalling software, cookies and temporary files stored by an Internet browser, third-party browser extensions and incompatible spyware or compu