Problem was occurring if the use loads in a composite block using 'load' from the file menu, then adds an example of the block to the system, and then deletes this block, and then clicks on the tab to try and bring up a view of the block.
Code Example
Fix Date
17/02/04
Fix Notes
The view of the block was being generated from the block that was added to the system rather than a copy. So when the block was deleted the view was trying to construct itself from an invalid pointer. The view is now constructed from a copy and the problem no longer occurs.