I have updated my Kirbysite to the last Kirby-Version.
But now if I want to save an article I get an alert window with the message > An unexpected error occurred
I think the problem comes from a plugin but how can I figure out whats the problem is?
Is there anything in the PHP error logs? Try to deactivate the plugins first, i.e. remove them from the plugins folder and check if the error persists. If necessary, remove fields connected with the plugins from your blueprints.
Edit: Which plugins do you use?