I am getting the above error each time I click on External Content Type in Designer 2010. It completely shuts down the application with this error in my Event Viewer. Any suggestions how to handle this? Everything else in SharePoint Designer is working fine.

Hi SharePoint4You,

So, first you should check there is no any anti-virus software in your environment. This is maybe caused by this kind of software.

http://stackoverflow.com/questions/334706/fatal-execution-engine-error-79ffee24-80131506

Here is a hot fix, you can have a try to install it.

http://support.microsoft.com/kb/913384

Thanks,

Jack