It's obvious that the problem is you have sticky mouse balls.
I can't find the original steps for cleaning your mouse balls but these might work just as well.....
A mouse for all seasons
Your basic mouse scrub can be summed up in three easy steps: pop, plop, and scrape. But before you pop, plop, and scrape, you should save your files. There's nothing worse than accidentally erasing your report because you got too frantic with your mouse cleaning. Clean 'n' Go, a free download, promises to turn off your mouse or keyboard for the duration of a cleaning.
1. Pop
Pop off the cover that holds in your mouse ball. You shouldn't need a screwdriver. Just flip the critter over in one hand and push the cover around using your thumbs. You can almost always find the proper direction molded into the cover.
2. Plop
Hold the mouse (ball up) in one hand. Cup the other hand. Turn the mouse over above that hand. Barring a severe soda or juice accident the ball should plop into your hand. Put the ball (heavy, isn't it?) into a spare dish, empty coffee cup, or pocket. Do not set it on the desktop. It will roll off onto the floor, where the cat will either ingest it or flick it under the couch next to the other 30 missing cat toys.
3. Scrape
I generally use a pencil eraser or my own fingernail. Essentially, you reach in and scrape the (quite obvious if it's dirty) ridge off of each roller. Purists claim that a cotton swab and alcohol do the best job.
Cleaning your mouse