Device Timeout

When I am trying to access the data from xPC Target, I am getting the following error in my MATLAB.

??? Error using ==> fread at 51
TargetPC1: device timeout

Error in ==> xpcread at 12
data_1 = fsys.fread(h);

Also, in the xPC Target, the following error comes.

ERROR : -23:device timeout

What could be the reason and how to rectify it? I am using MATLAB 2011a and xPC Target v5.0