Desktop problems

[mlafuente]

I have a Macbook Pro and have purchased a MB169B+ portable monitor. Everything works fine but when the laptop is connected I can't do anything on the Mac desktop. I can't drag files or right click, but on the laptop I can, it's like the Mac is locked. Some help?

[mlafuente]

I just discovered that if I turn off active corners I can now use the Mac desktop. Any solution to be able to use both?