Sharepoint 2010 Question : Error while deploying wsp.

When I tried to deploy the wsp's using managment shell (power shell scripts) everything looks good.

When I go and take a look the "manage farm solutions" thru sharepoint central admin, I see the deployment failed in one server.

Error is

Cannot add the specified assembly to the global assembly cache : xxxxx.xxxxx.dll.

Can you please let me know what could be the reason.

Note : I have two app servers and two web servers setup. The deployment is sucessful in 2 apps servers and 1 web server. Only one web server deployment is giving error.

Thanks

Ravi