Did something with macros, now I get an error every time I start LibreOffice (screenshot attached)
how to fix the error?
Maybe the macro that you want to run is no longer there? Did you reset the user profile, change the name of the macro, change the security settings of LO (not allowing macros might have that effect, I didn’t test it)? Select Tools - macros - Organize Macros, navigate to the relevant folder (Standard - LibreOffice, etc.) and check that the macro is actually there.
If it is there, please edit your original question to add that information, or post it in a comment. Thank you. 
The macro is registered to be called when LibreOffice is loading but you deleted the macro.
Remove the call from Tools>Options>Customize… tab “Events”
It is not there, and I don’t know how to stop this error
Sorry, I mean Tools>Customize… tab “Events”. There you registered your macro for execution when some event happens (such as “Start Application”)