How to store data in a variable in M-files

One easy option could be to use a multi-line text property on the drawing metadata and record the error log in that property. So each time there's an error, append the reason to the property as a new line. Of course the feasibility of this depends on the information you need to record (is it just a short description or some more detailed error data).

The property permissions can be restricted so that only the relevant users see this error log on the metadata card.

If a text property is too limited, you could create a separate object type where you record the error details and tag these objects with the original drawing. Then you could view the error objects related to the drawing via the object relationships.

There are also other approaches depending on what information needs to be recorded and where you need this information later on.

Right, and how can we insert the data into a specific property each time it passes through a certain state, would it be possible to do this via admin, or does it require some programming or scripting?

You may be able to use for instance the Property Calculator add-on for this if you don't want to write any script or code yourself. It's not directly possible with the workflow configuration in M-Files Admin.

Thank you so much Joonas, you helped us a lot!