This is a known issue with Machine Control 1.0.1 and Pro Tools 5.3. It occurs after doing anything (including removing or authorizing a plug-in) with a PACE iLok authorization key, quitting, and then relaunching Pro Tools. Pro Tools will then hang on loading Machine Control at the next launch.Currently there is no workaround except to remove the Machine Control extension from System Folder>DAE Folder>DAE Extensions. Otherwise, a reboot is required. This issue is resolved in Pro Tools 5.3.1 and higher.