How to turn off this line splitting up my screen?

[theoD]

It may have to do with multiple column layout options. I can hit Alt-2, 3, 4 to add more columns, but when I’m back to single column this line persists. Do you know how to turn this off?

Thanks,
Theo

[jfcherng]

It looks like a ruler. Did you check rulers in your user preference or Menu > View > Ruler?

[theoD]

Yup, that’s it! Thank you very much for your help!