Problems creating PSSession remote script execution

Hi,

I'm creating a script to remotely connect to a Exchange Server to create a mailbox using PowerShell from a webapp. The scripts starts with this line for creating the PSSession:

$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri http://[FQDN]/PowerShell/ -Authentication Kerberos

When I login in the server and I run the script directly works perfectly, but when I run from the webapp I get this error:

[server name] connecting to remote server failed with the following error message : Access is denied.For more info, see the about_Remote_Troubleshooting Help topic
+ CategoryInfo          : OpenError: (System.Manageme....RemoteRunspace:RemoteRunspace) [], PSRemotingTransportException + FullyQualifiedErrorId : PSSessionOpenFailed

I have this script deployed in a Exchange Server 2010 and works well from my web app using the same credentials. Could anyone help me understanding what's happening?

Thanks in advance,

Ignacio