After aggregate four ethernet between NE40 and MA5200, the old netcard on PC underlying NE40 is unavailable, while the new one can go on line.
Change the malfunction interface on NE40, the problem is solved.
Aggregate 4 ethernet interfaces between NE40 and MA5200, Vlan transfers. After interface aggregated, NE40 will perform HASH algorithm according to source MAC, destination MAC, to ensure to travel through which link. So the links where the traffic travels through is various because HASH algorithm is various.
One interface integrated on NE40 or MA5200 is error, but the interface is UP, so the aggregating interface cannot be auto-switched. While the PC sends packets from the old netcard s,NE40 also porfroms HASH by the old netcard MAC to select the error interface , so the sent packets still travel through the malfunction links, finally, the old netcard cannot communicate with the gateway; after changing another one, because MAC changes, HASH will switch to another normal link, so the new netcard can go on line.