who can help me to solve this problem. Now I can only open an other catalog. But not this one,.And this is the main-catalog.
So I am a little bit desperate.
Which version of Lightroom are you using?
With Lr closed go to the location where your Lightroom catalog resides(By default it is Pictures/Lightroom)
Delete the .Lock file with the same name as your catalog.For instance in the Picture below it is Lightroom4 catalog.lrat.lock
In your case it will be Lightroomcatalog.lrcat.lock.Delete it
Let us know if that helps
Wonderful !!thanks very much.