Like a lot of other people I am having major problems with v1.5.
My main PC, which i've been building my library up on since Rekordbox became free, is running 1.5 with no problems at all (Win Vista x64) but it's not in the same room as my new CDJ900s so I have another PC in that room. It was running XP which v1.5 didn't work on, so I upgraded to Vista x64 & got it work only when installing RB before anything else. However, I need to use my decks at other venues so I have to rely on my laptop which runs XP, & lo & behold it didn't work. I reloaded XP & it worked for a few days before the usual scenario of crashing as soon as you try to run RB.
Now here's the key point. My CDJs came with v188.8.131.52a on the CD which I loaded on to my laptop & it worked fine. It's been mentioned here that you can't downgrade RB & expect it to work. However, on my main PC (Win Vista x64) I unistalled v1.5 from the add/remove programs, I didn't reboot the PC nor do anything else (ie left all the files in the pioneer/rekordbox folder). I then installed v184.108.40.206a & much to my surprise everything was still there, all the files were analyzed & it was all good to go. If it's of any relevance my entire library of around 3000 tracks are in wav format not that it should make any difference.
btw, I haven't tried this with v1.4.1 as I haven't got it.
I'll happily furnish anyone with v220.127.116.11a if & when Pulse or anyone else in authority says it's OK to do so. Also if anyone has v1.4.1 to hand I'll try that & see if it works.