Thanks for your help on this. This has sorted the issue.
Although, it does seem that this is a prime example of how your product doesn't work. It is billed as a "drag and drop" product, and yet I have have to patch code, making it incompatible with any hotfixes/upgrades you have.
I'm sure we won't be updating the site however, as this and the numerous other issues are scaring the hell out of me.