in addition, i have tried to open older catlogues with the same result
You are trying to open a catalog that was created in Lightroom 6 or Lightroom CC 2015 by using Lightroom 5. You cannot open these catalogs in Lightroom 5.
You need to find the version of Lightroom CC 2015/Lightroom 6 on your computer, and open that, then use the menu command File->Open Catalog to select the catalog you want to open.
Fortunately, there is a quick and easy solution to this problem. If you encounter this error message on startup then all that you need to do is to tell your computer to open this Lightroom Catalog (your .lrcat file) using the most recently installed version of the Lightroom Application.
In the Mac world, this is best done by right-clicking on your .lrcat file and using the <em>Open With</em> command. Windows users will find the same command with a right-click although so far I have mostly seen this error on computer's running the Mac operating system. See the video tutorial below for more assistance resolving this issue.