in fl studio 10, my buffer size is great, my pc is powerful but still sometimes it occurs and i dunno why, does anyone has any ideas?

i had this with my old sound card, with my new audio interface and it still doesnt change. already when played in the DAW in some situations, not always and no, no distortion effects, heavy limiter etc. at all.

First, some presets in Omnisphere are too loud and clip inside the plugin right away. I use to lower the output slider at the upper right corner.

Second, big buffer sizes are sometimes bad for sample based instruments with DFD (Direct From Disk streaming) like Omnisphere or Kontakt. Try lowering your buffer size to see if that helps.

Third, Omnisphere comes with many advanced options to fine tune the performance of its audio engine. Check the "System" entry in the html manual or ask Spectrasonics support for guidance. If you have a lot of RAM you can even disable streaming.

I find that the problem may very well be FL Studio.

Some plugs I use in FL Studio click and glitches like h*ll, but when I load them in Sonar X2 instead they work just fine

An example is PolyKBII Player, almost impossible to use for me in FL Studio because it glitches so badly, but the plug runs smooth in Sonar X2. Same PC, same soundcard, so what can the reason be?

If you go into Instrument Properties and set Polyphony to 1, it helps. You can still play/hear chords, but it will reduce CPU. Just make sure you have the "Notify Plugin while Render' notch checked.

PS, 'Use 'Fixed Buffer Length' also in Options.

Maybe it's FL, but I've encountered the same problems under SONAR. It seemed to be a case of disk I/O not keeping up, perhaps due to memory getting very low. The solution for me was to do a real-time bounce on Omnisphere tracks, but not being a FL user I don't know if you have that option or not.