I upgraded to the latest 5.6 a month or so ago (whenever it came out I guess) and this "Server Busy" dialog loop when starting Lightroom started occurring shortly thereafter.
If I repeatedly click "Try Again" or "Switch To" things eventually start to work - no consistent pattern or timeframe that I can detect.
PC hardware is a Supermicro chassis with 2x5430 CPU, 20 GB of RAM, 2GB Seagate 7200 SATA drive(s) on an Areca RAID controller (in JBOD) for RAW image and catalog storage with LR running from the system's Win7 64 boot SSD and the LR cache set to a directory on an otherwise unused older 60GB SSD; oh, plus a pretty nondescript Radeon video adapter - can't remember what it is but it's nothing special. There is no resource problem going on - this happens when only LR is running as well as under normal use; perfmon shows almost zero CPU and tons of RAM free.
Any tips to debug this? It came on all at once, and I'm about 90% certain it was directly timed with the last upgrade. I see some similar (but much older) threads on this type of subject, most were suggesting older hardware, although some said catalog corruption caused it.