Cannot update price once product has been created

Hi,
We created a product and set prices in different currencies. We have your plugin set up with “manual price” so we can set prices ourselves in different currencies.
Now the product has been created, it wont let us update any of the prices. When we go to the admin > edit product > update the price in euro for example > save > the page refreshes, and the old euro price is still showing (not the new one)
What’s going on ? Please help !

Many thanks
Greg