You might be experiencing this issue which has been causing CS4 updates that patch files (instead of replacing them) to fail on some Windows machines. This issue, cause, and solution are documented here:
Please note that the ACR 5.2 update was susceptible to this issue. We believe the ACR 5.3 is not. However, if a previous update of ACR failed due to the root cause, then it can leave your files in a state which will prevent future update from working, simply because they don't find the files in the expected state. In which case, you need to do the complete solution, which involves a clean re-install (sorrry :-(
There is no need to deactivate the product if you are going to re-install it on the same machine. The activation server has a unique ID for the machine, so if it gets an activation request from a machine that's already one of the two allowed activations, it doesn't take another activation slot.