All of a sudden ?? instead of year in citation references

[racoon]

Hi,

I am using BibLaTeX as described on 
https://wiki.lyx.org/BibTeX/Biblatex. I think I have cut an pasted the 
LyX note containing the "BibTeX Generated Bibliography" and all of a 
sudden all year numbers are replaced with ?? in the work area. The 
output is fine though. Also in the citation dialog there are no more 
year numbers in the reference preview. How can I get the year numbers back?

Daniel