compatability of Endnote 5x with 6x

I work on both versions of endnote however I have noticed that when I try to open a library in 6x that was created in 5x, I get an error message which any further use of the program and I have to force quit.

Any suggestions on why this might happen?



I don’t get that, although I do notice when jumping between a library openned in X4 and then in X6 and back again, the library PDFs get reindexed. Perhaps there is a corrupt PDF?