The NeoLoad documentation says "Before running a test, it is strongly advised to close the antivirus installed on the Load Generator machine. Keeping the antivirus alive may alter the relevancy of the test results." What specific problems could be encountered if antivirus is running during a test?
Antivirus programs can sometimes put locks on open files that the LG's are using, causing problems with sending and receiving data and files. This can cause response times to be skewed, or cause the LG to consume tremendous amounts of CPU resources and high memory usage, which can effect things indirectly. Basically, it is just best to disable the antivirus temporarily during testing to avoid skews in results or the test from even working and having errors, consuming resources.