Quotes to invoices - change??

We have always done our quotes in desktop and changed to invoice once a purchase order number is received.  Invoices have been emailed out of the web version (better ability to format forms)- the only thing that used to pop up was the invoice was read only as it had been done on desktop - fine no problems, we'd send the invoice off via email.

On 18/6 something changed and if the quote & invoice was done in desktop, emailing it from web is not an option.  Now we get :

"This invoice is read only because the tax amount was overridden and this feature is not supported."

Nothing has changed - my only options in the web version are record payment or delete on top RHS - prior to that I had the full usual options - preview, share, save.  

These quotes are pages and pages long, invoices from desktop are not what we want.  

Short of re-typing the whole thing has anyone noticed the same and have worked out a work-around?  

Nothing is overridden tax wise, it should be a seamless transfer between desktop version and web version.  All items are tax inclusive. 

I'm stumped and its impossible to get onto MYOB help at the moment.