Timeout error with MCC USB 1208FS

Hello everyone, I'm acquiring data with a MCC USB 1208FS on Matlab using Simulink. The digital output block works fine, but i have problems with the Analog Input block. Every time I launch the acquisition, the following error appears:

Error reported by S-function 'sdaqai' in 'dataacquisition/Analog Input': A timeout occurred during GETDATA.

I have tried several times to change the samples/sec and also the block size (options available in the Analog Input block) but nothing changed. I also tried to use older versions of Matlab (Matlab 2010b and Matlab 2008b) but nothinkg changed. What can i do?

I'm using Matlab 2014b (32 bit version).

Thank you,

Fabrizio