Never heard of Huawei - I'm used to Cisco and Nortel DWDM muxes, nevertheless ...
Check the optical power levels coming out of the DWDM multiplexor's transponder using a power meter. Make sure both your line card and the transponder are 1310 nanometer wavelength (they probably are) and that both are either single mode or multimode fiber.
If the power level looks high (check your specifications, but anything higher than -8dBm is probably too hot), pad your Rx port with a fixed pad attenuator and see if you get protocol up. Whomever built your DWDM network may have a few handy - 5 or 7dB should get the job done.
Of course, you'll need an OC-48 line card on the other end, and you'll want to repeat the process there if the symptoms are the same.
Hope this helps.
