FWIW, we encountered this issue and found a work-around that might just be unique to our situation or it may help others. The issue for us was related to Selection Layers being used in old, saved off LYRX files. We seemed to have been given a pass in the various 2.9.x and the initial 3.0 releases, but ArcGIS Pro 3.1 did not like that we had these specified in our LYRX files. In ESRI's defense, that link states these should be used temporarily, but the vague error popping up w/ layout exports really tripped us up for a while and made little sense with the layout not even having that map/layer in it.
Anyway, if you think you may have used a selection layer in your project, clearing that out might fix your issue. Here are some steps we used to allow for layout printing:
- Open a Pro project giving you trouble.
- Right-click on a suspected layer in the TOC that might be a "Selection Layer", and click the "Properties" menu choice.
- In the "Layer Properties" dialog that opens, select the "Selection" choice in the TOC within that dialog. I think ESRI calls these tabs (i.e., the "Selection" tab).
- Toward the end of the listing of properties, you should see a check-box that states, "Clear selected features to access all features in the source data". Check that box, and click the "OK" button. If you don't see that message/check-box, this isn't a "Selection Layer" and you'll want to go back to step #2 above with another layer in your TOC.
- Save your project. IMPORTANT: Closing the project and re-opening sometimes does the trick and you can export layouts here. If not, try the following steps as well.
- Click the "Project" menu choice and then click "Options".
- In the "Options" dialog that is displayed, click the "Display" choice in the TOC therein.
Click the button toward the bottom that states, "Clear Cache Now". - You'll see a confirmation message, and you can click "OK" to the message, the "Options" dialog, and then any "Save changes..." message that pops up.
- Your project should be restarted, and, at this point, you should be able to export your layout if indeed a miswired "Selection Layer" is the culprit.
Hopefully this helps someone as I know how frustrating this bug is, but maybe our situation was just one of multiple ways this error message manifests.