Event for tax entered incorrectly

Hello,

We have an event that was entered for tax incorrectly (without task #)  that was billed out on a AR invoice.  The invoice has now been cancelled however we can't back out the event as it has been processed.  This event is preventing  new lines from being distributed to the g/l therefore impeding new draft generation.  The draft will not pick up all revenue on the project.

Any ideas?

Help would be great appreciated!

Thanks

Marie