I got this error while opening CRM 4 !
The solution was to run the following command
which could be found at
C:Windows\Microsoft.NET\Framework\v3.0\Windows Communication Foundation.
Followed by an IISReset.
However in few cases to resolve it, it requires reinstallation of IIS.
ServiceModel Registration tool with -i option
Registers this version of WCF and update scriptmaps at the Internet Information Services (IIS) metabase root and for all scriptmaps under the root. Existing scriptmaps of lower versions are upgraded to this version.