Real Time Scan Stopping/slowing Downloads Progress

Hi I have a problem with my fully updated and purchased copy of Bitfefender Total Security 2009.Once I have the real time scan enabled my downloads sometimes reach 30% 50% sometimes 99% and stops there as well as it lowers my download speed dramatically...once I disable the real time scan and resume the downloads it completes 100%.....and I experience no problems once I leave real time disabled.I have tried different OS versions even re-install my OS several times i even tried different download managers and still the problem exists.

Any BD Technicians help me with solving this problem... please