When working in the program you receive the following error:
“License error. Your license is invalid. Please contact your local authorised AutoCAD dealer.”
This may be followed in some cases by an error "Unhandled e06d7363h Exception at 7c812a5bh".
The "License is invalid" and the "Unhandled e06d7363h Exception at 7c812a5bh" are common errors which result from out of memory scenarios.
If the memory footprint for acad.exe goes over 2GB (regardless of how much memory is in the system) Windows will terminate it. This is a limitation of 32 bit computing.
In the Task Manager you will often see the memory usage for acad.exe between 1.2~1.8GB during these crashes because there is a lag in the memory reports from the Task Manager.
In 32 bit operating systems, AutoCAD (and other applications) is limited to 2GB of total memory usage regardless of how much memory is installed in the machine.
The amount of memory that can be allocated to AutoCAD and other applications can be increased to 3GB by implementing the 3GB switch in Windows. See Enabling the 3GB switch on Windows Vista, Windows 7 and Windows XP for instructions.
Note that in a 32 bit environment this is as much memory as can be allocated to AutoCAD, so if the memory use pushes over even the expanded 3GB memory limitation you may need to consider moving to a 64 bit environment. In a 64 bit system the memory allocation has been increased dramatically and out of memory scenarios will be uncommon if they occur at all.