I also got the same problem. pslauncher runs fine, pslauncher2 won't run. The client 0.5.6 itself runs fine if it's started directly (psclient.exe), or from the "old" pslauncher.
Neither running pslauncher2 as administrator nor using one of the compatibility modes helped to get it running. And it's not possible to run a 64-bit program "as 32 bit" like Tessra said. Or did you want to say that the 32-bit version isn't affected?
My system: Athlon II X4 640, 4 GB Ram, ATi Radeon 2900 Pro, Windows 7 Professional x64, PS x64