Photoshop every now and then shuts it self up when it comes to importing other windows clipboard data. In that case just test if you can copy paste from msPaint to PS, and it that fails just restart Photoshop.
It is very annoying but PS had that already for many releases
As for limits: There are limits what windows can carry around at least from my experiences with dotNet which hooks into windows and lets you set the clipboard bitmap. At some point under XP 32 bit I couldn't carry 4k maps over or something above that, but these days most of the maps are 2k which just work fine on any windows OS.