MyBook 2TB drive full error msg

Hey, thanx

…but, as I said…I am .“able to create folders and transfer files successfully from my internal  hard drives.” if I save it there first.  My question is Why does this happen?  I should not have to go thru this extra step.  I have a Sony video editing program and also a PaintShopPro which  the WD has no problem saving files directly from the program.   I also have a 1TB MyBook hooked up where this does not happen.  Have I neglected to install some sort of software?.  The drive did not come with an install CD…I just plugged it in and fired it up