Warning! Render did not complete!

Hello!

I am constantly getting the error: Warning! Render did not complete!

The error only occurs, when adding a Saver (SV-node) to the end of the comp.
If you chose before the final Saver my final Merge node... and just render it to the RAM.

All frames are fine, and the comp looks perfect.

However, I am not able to render the final shots, because of the Error message when adding the saver node.

Anyone any idea what issue that could be?

Thank you very much!

Two questions:
1) what does the console give as a reason for not being able to render?
2) you did enter a (different) filename and codec options for the file that needs to be saved?

I've also had this problem when the file is open in another app.