ORAMED-01003: Namespace prefix 'dvm' used but not declared

Problem:
Creating an assignment in Mediator 11g to a SOAP header (e.g., endpointURI) looks as follows:

Even though the DVM lookup expression is syntactically correct, when executing this service, you may get the following error:

ORAMED-01003:[Invalid assign source expression]Invalid source used while assigning. Check if source expression are valid. ["dvm:lookupValue('oramds:/deployed-composites/default/XrefDvmFiles10g_rev1.0/AhmedDVM.dvm', 'Domain1', $in.payload/client:process/client:input, 'Domain2', 'US')"]Possible Fix:Modify source for valid expression Cause:Namespace prefix 'dvm' used but not declared.

Solution:
Open the expression builder, locate the 'lookupValue' function under 'DVM Functions', and double-click it to insert it into your expression. Then insert all your data manually, and redeploy.