Your best bet is to leave it. Don't shut down your computer or restart the agent, because that will cause the work unit to lose a small amount of work.

The non-deterministic algorithms used by the science applications take varying times to complete. Sometimes, the progress estimate is wrong, and you will see the percentage stick (or, on very rare occassions, go backwards). It is also possible for the algorithm to fail to converge. However, the software will eventually detect this and move on.

Remember, a longer work unit will net you more points, and all results are equally valuable to the scientists.