I have never seen so many bugs in Adobe LR 6 non-CC version.
Besides the "Server Busy" error I have encountered a blue screen with an white X and no picture. I have exported a photo file and the file exports correctly but I get a Video Not Supported in the Develop mode. I have had a gray area over a photo with what looks like a flower burst. I can go on and on but these are the ones I've found so far.
I don't really see a significant difference in LR6 vice LR5. LR5 are more stable and predictable.