USART Interrupt not being called

Hi I have written a small piece of code to transmit and receive data through a USART using DMA. The problem I have is that my interrupt handler is not being called. My code works fine when used in other projects not using the FreeRTOS. But when I tried to include in my new project is does not get called, if I read the registers I can see that there is an interrupt pending, just not being called. I am using the Cstartup.s79 file from the serial demo project. I am using the IAR compiler. I am using the Atmel sam7s. The code is written in c and c++. Thanks