Error when exporting JPG/PNG

[xtom]

In Designer Pro X sometimes when I go to export a JPG or PNG a (windows like) error dialog popsup...

An unkown error has occurred while accessing an unamed file

then after clicking by this another designer pro dark grey dialog pops up...

An error occurred (unknown) when opening the file:

If I go back up to the export buttons on the toolbar after these errors or even go to the export option in the file menu they are all disabled and I can't export without restarting the program.