We need more information if we're going to help you.
What is the exact text of the message that you're getting? What operating system? Has After Effects CS5 worked for you before on this computer? If so, what has changed since then?
For starters, check out this thread, which has some possible solutions:
This is a new reply to an OLD question. Sorry....I just encountered the problem today trying to apply an Adobe update. But maybe it will be useful to a future reader searching on the same problem.
Most of the replies, even from Adobe people, say to just terminate the dynamiclinkmanager process. I hate terminating any process that I don't know what it does. Maybe the thing has important files open? What could happen if I kill it?.
In my case, I made sure to "Quit" all open Adobe applications (Br, DW, Ai, Ps, Pr, etc). After closing these programs, dynamiclinkmanager "disappeared". So I would suggest making sure there are no open Adopbe apps. If that doesn't work, then nuke the sucker :-)