SQL Counter Problem

Is there a limitation with the SQLCounter routine using a value above 2,148,000,000 in the checkfield ? As if I set this value to anything below this figure the routine works as planned however if I go above this value it rejects the user as no available time. I am trying to use the sqlcounter to check to see if the user has available bandwidth and if so give them access, but this now limits me to this value. I am using the freeradius port for cygwin, can anyone help me out with this as I need to set this figure to above 30Mb value