Please tell us word for word what the error message says.
You have several good guesses in this thread, but that is all they are--just guesses. It is not helpful to tell us you get "some kind of error message"--when you say that, all we can give you are guesses. If you tell us what the error message says, then we don't have to guess--we can tell you exactly what the problem is.
Tacit,
as is frequently the case w/ your contributions to threads here at TS, this is so clearly stated and so so 'right on target' that I am tempted to lobby for it to be made into some kind of rule, or at least a strongly worded guideline for future posting here at TS. Maybe something like this:
The more detailed a description you provide of your problem or issue, the better we [collectively] can help to focus on the exact problem and provide a solution; if you receive Error Messages or Dialog Boxes, note and report the precise wording; describe in detail the steps required to produce the symptoms; and in many cases, the Mac Model and amount of RAM installed, version number of system software [e.g., OS-X 10.3.9, 10.4.11, 10.5.5], and application [Photoshop CS2, iTunes 7.5, Firefox 3.0, etc.] can be especially relevant to solving your problem, so please include this type of info if you know it.
In most instances, without detailed info, all we can do is speculate about the source and solution to your particular problem, so if you'd like us to provide detailed troubleshooting and problem-solving advice rather than theories or guesses, help us to help you.Kb