If this is the problem (error code 23), this is a known bug. It will most likely be fixed in the next update. For now, as a workaround, you can make a simple change and try exporting it again.
For exporting pngs, the "error code 23" problem is a known issue, which is being worked on, and I already offered a temporary workaround. Saving the project as a .pxo should still work.
