Also, if your driver version is still 1.0.1, the latest version can be downloaded from here:
http://www.roland.com/sup...=downloads&p=UA-55

You can get much lower latency with the same buffer setting.

It sounds like a cache or memory problem. But really I you want to set up a loop you should convert the audio or midi clip into a groove clip then stretch the groove clip to the length you want. To create a groove clip right click on a clip then go to Clip Properties->Audio Stretching->Enable Looping. Next hover you mouse of the end of the clip. When your your mouse changes to a square drag the clip to the new length. If the original clip contains a loop you will see repeating audio patterns in the wav pattern. You can allways tell a Groove Clip because the edges will be round. You can learn a lot about Sonar from the official book Sonar XX Power. Here is a link. http://www.amazon.com/s/?_encoding=UTF8&camp=1789&creative=390957&field-keywords=cakewalk%20sonar%20power&linkCode=ur2&rh=n%3A283155%2Ck%3Acakewalk%20sonar%20power&tag=sulaimanthewordsmith-20&url=search-alias%3Dstripbooks. Scott R. Garrigus is the author and he has a support form for DAW's where he answer lot's of questions. http://www.digifreq.com/digifreq/discuss/.
 
 

Chris:
 
If you're recording MIDI rather than audio it may be that the MIDI buffer setting is too low. In fact this is probably worth doing anyway even if your problem is with audio.
 
Go to preferences/advanced/MIDI playback and recording. If the setting at the bottom under "playback" "prepare using xxx Millisecond buffers" is less than 500 set it to at least 500 (the default is 250 which causes lots of people all kind of strange problems, especially when loop recording as Sonar seems to run out of breath and fall over itself).