You can try the Hide Submit moddule:
Some users accidentally click the submit button more than once while waiting for their post to be saved. In some cases this may result duplicate postings or duplicate e-commerce orders.
There are few ideas on how to solve duplicate postings but none is perfect. One of the solutions is a bit of jQuery to hide or disable the submit button after it has been clicked and replace it with an informative text such as "Processing..." .
This module wraps that jQuery code and provides some options. Of course this, too, is not a perfect solution as it requires Javascript to be enabled. For browsers with Javascript disabled this module will have no effect at all.
