Line to Pad Spacing DRC .050mm / .050mm Design

Hello,

      I am working on an very dense design using .4mm pitch BGA's with .250mm pads.  In order to escape the part within the desired layers we have decided to reduce the min line width and spacing to .050mm and .050mm underneath the package.  When I try to route between the pads the trace jogs up by .004mm and generates a DRC.  Why wont the trace route straight through the pads? Any help would be greatly appreciated.

Thanks,

Clint