"No free license" error in Crystal Reports

The following error message occurs with some reports of our Crystal Reports application, when you try to open them a second time.

"A Crystal Reports job failed because a free license could not be obtained
in the time allocated"

It seems to be a problem only with some reports (with a lot of data in particular). Other reports work without any problem. But once the error message appeared, all reports will fail.

Can anyone tell me how the li开发者_运维问答censing mechanism of Crystal Reports works?

Where is the "free license" obtained from?

Can this be a time issue due to the amount of data?

-- edit --

From what we learned in the meantime, it seems to be a problem only with reports that called a particular long running PL/SQL package in the report command. And Crystal somehow doesn't like calling that twice.

And i guess the error message is just a secondary symptom and not the cause.