First result:
The crash is happening due to a stack overflow exception in GUIGroup.cs: GetFocusControlId()
Obviously the children aren't handled nicely.
Good news is that the issue is not related texture management, phew... cannot be as bad as it would have been. Are there any recursive calls on that are that could cause easialy the stack overflow?
There are at least two places with recursive calls that would stall MP. The focus handling however is that complex that we have to wait for someone who worked on that for a safe fix. At the moment it looks like these skins have a bad focus handling where control groups (their members) rival to get the focus. Maybe some animations cause invalid focus changing. I don't know however if this can easily be prevented by MP's skinengine...