I guess you have encountered a bug. A credit limit of 10000 would mean a block when the balance + current invoice exceeds 10000.
This is fixed in release 2.3 by given the current credit information for the customer on the form. You see when the limit is below 0.
For release 2.2.X you could set the customer on hold. We do not maintain bugfixes on 2.2.x any more.
/Joe
