it's me again !
After reflection, I now further remember 2 other errors, I made that very likely hindered UCAC 4 from working.
I downloaded from here http://casdc.china-vo.org/mirror/UCAC/UCAC4/ (Chinese mirror of the UCAC catalogue, because the guy in the German link mentionned in a previous mail is saying that there are checksum errors in the Strasbourg link; I found this link here: http://www.astrosurf.com/c2a/english/information.htm).
1. Did you also put the index files in the UCAC catalogue ?
In the above link are two sublinks beginning with "U4":
U4b (b = binaries)
U4i (i= index)
U4b contains the 900 files of the UCAC4.
But you also need to download the 5 or 6 files from the U4i sublink (index files) and put them into the UCAC4 folder.
2. I had a very nasty error within the 900 files !
I had resized the explorer window in such a way that it always showed exactly ten files. And I only controlled by looking at the end of the line, i.e. whether there was always a number dividable by 10. But in one line (of ten files) I had downloaded twice one same file and forgotten another in the same line (very nasty thing !). This might also have been the reason why it did not work.
Kind regards !