Hello,
thanks a lot! It worked for me and the yellow warning changed to red alert similar to the one in the blog you cited :-)
In my case, the cause was not inssuficient disk space on the server's disk, but the fact vCenter checks for the size of the database file in the filesystem, not the real amount of data in it. So if I have sql express with 10 GB limit, the database file is 9.2 GB and sql server management studio shows the real data is just 4 GB in it, the alert is still issued. Shrinking database file was the final solution, which means that operation could be needed run periodically.
Thank you very much for your help.
David