I just solved the problem my self. I just download through the x-modem (not 1k-Xmodem) the Ver 7.52 dwl.dwl bootloader and afterwards the R7.52.0_fxt009.dwl from the http://source.sierrawireless.com/resources/airprime/software/firmware-package-7,-d-,52_open-at-version/. It is working fine again. I restarted using AT+CFUN=1 after downloading dwl.dwl file and downloaded the R7.52.0_fxt009.dwl again restarted using AT+CFUN=1.
Hope this would help someone 