Error uploading file: server did not respond

After uploading a file in the client (filedocument is saved) we want to process the imported file with a microflow button. In development (laptop) the is no problem, but at the customer site (the application runs at Mendiz) we get the following message (not always): An error occurred while uploading a file: the server did not respond. Does anyone have an idea what the problem can be (and how to solve this)?
1 answers

What does the log say?? Do you have a stacktrace?