VIclose() doesn't work

hello everybody !

i'm working on visual studio 2010 with the VISA library and my aim is to take the control of an attenuator.

I can easily pass it on remote mode with the ViOpen() function in  this few line:

ViSession defaultRM, instr;// Declares type ViSession variables

ViStatus status; // Declares a type ViStatus variable

status = viOpenDefaultRM(&defaultRM);// Initializes the system
// Open communication with Serial Port 2
status = viOpen(defaultRM, "ASRL2::INSTR", VI_NULL, VI_NULL, &instr);

but i can't stop the remote mode with the ViClose() function, it doesn't work...

status = viClose(instr); // Close down the system
status = viClose(defaultRM);

help me please !!