Deployment solution can only image 2 machines at any one time.

We have several site servers with deployment soltion installed in our company. All but one can image many machines at a time. I have seen up to 15 machine being imaged at one time. At one of our sites they can ony do 2 at a time.If they try to do more it fails an earier job. Is there any special conguration that needs to be done on the server to allow more? All are using the same global settings. Thansk in advance for any soltions