Column view in Finder

Ok, so I had this problem before, but it sort of fixed itself, not sure how, but it has just resurfaced again. Normally, in Column view you can drag the width of the columns and make them as wide or narrow as you like. However, mine right now has the double-lined bar with the slider instead of single lines..... and I cannot adjust the columns... Not sure what this is or how it happens. Not sure if I am being clear enough in my description, but I am adding a screen shot to help.

Anybody else have this and any idea how to change this? I can't find anything in Prefs or View Options or anywhere else. I have had to Relaunch Finder from the Force Quit Applications window, so I don't know if that has anything to do with it. Have also restarted my MBP as well. I had posted a discussion about this before and don't remember if anybody answered it or not, but I can't find it.

Thanks for your responses.