>>>Does the custom property already exists when the error happens?
>
>Nope, it happens when the property is created. If I add the property manually to the VCX then the error does not occur (errors on next line which is same code but for height), so it must be something to do with the creation of the property.
>
>Gary.

Gary,

Did you try to put some code in Width_Access method to see if the problem is related?