My sister cats are fighting....AGAIN!

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I do not understand this behavior. It is kind of a long story, but...we got two sister cats when they were kittens. Well after a while we realized we could not trust them on our carpet, as they were peeing everywhere. We started keeping them in the unfinished basement where we visited them everyday. We hated to do it, but we couldn't let them ruin our home and we didn't want to have to get rid of them. Well time went on and soon we were re-finishing our basement and this was too stressful on the cats so we brought them upstairs and now keep them in a kitty condo, which they don't seem to mind as they are in my office with me all day and I let them out alot of the time and they pretty much stay in my office anyway. Their litter box is in the condo along with beds, food and shelves for them to lay on. I needed to give the background info in order to ask my question. They have been out of the condo for a couple weeks now, they are able to come in and out at these times, but today I moved furniture around and had to lock them in and ever since then they haave been growling and hissing at each other. they did this when I first got the condo and I was told they were going through a period of stress, but now? I don't know why they are doing this. Once I was done getting the room in order, I let them out, again they can come and go, but the one who was in the cage growled and the other one. This got me worried that the second one would not be able to go in and use the litter box due to the other one hissing and growling, so I put her in and locked them both in just to play it safe. Now the growing has not stopped for about 20 mins. Sorry this is so long...but does anyone have a clue about this behavior??