Internal Server Error when creating new posts

Hi – I’m getting this error page whenever I make a new post or page – just for new ones (this doesn’t happen when editing/updating existing posts/pages):
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Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
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It’s strange because eventhough this error page occurs, if i click the back button on the browser and then go to my list of posts, i will see that the new post/page has been created – however, this error page is annoying me now, so need to figure out why its happening and fix it.

Appreciate some help.