OData url conversion filter query

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OData

I have tables DEPatientVisit and DEPhysician

i need to filter the data based on StimulatorGourpId of DEPatientVisit. what i tried for this one

localhost:33396/FalconCPDataService.svc/DEPhysicians?$format=json&$expand=DEPatientVisits&$filter=DEPatientVisits/StimulatorGourpId+eq+guid%27F321EDAB-14C6-4FF2-9485-00ABD176EBC4%27
Exception :

it gives following exception "{"odata.error":{"code":"","message":{"lang":"en-US","value":"The parent value for a property access of a property 'StimulatorGourpId' is not a single value. Property access can only be applied to a single value."}}}"

the reponse of DEPatientVisit there is no nested values

{"odata.metadata":"localhost:33396/FalconCPDataService.svc/$metadata#DEPatientVisits","value":[{"VisitID":"f321edab-14c6-4ff2-9485-00abd176ebc4","PatientID":"c588df3b-9ea4-439b-9ab6-968a793dad2b","StimulatorGroupID":"b08d89e2-7dba-48ce-9430-282501397550","PhysicianID":null,"UserName":null,"PainMapID":null,"VisitDate":"2014-02-19T10:18:42","VisitReason":"usLro4OooDlMNJuWZHqeSXEKFwphz3Y9dvUr37RxHFz0h86aCImdsxUjuMWX64RG","Diagnosis":"7if/VTG/jeRgg0RjGp9Uzbi5iSglBgw59CwJKXcnk5E=","ClinicName":null,"ECModel":null,"ECSerial":null,"ECType":null,"ECFirmwarePN":null,"Notes":"","StimulationOnVAS":0.0,"StimulationOffVAS":0.0,"CRC":47851}
i tried like this

localhost:33396/FalconCPDataService.svc/DEPhysicians?$format=json&$expand=DEPatientVisits&$select=FullName,DEPatientVisits/Diagnosis,DEPatientVisits/VisitDate&$filter=DEPatientVisits/any(v:v/VisitID+eq+guid%27F321EDAB-14C6-4FF2-9485-00ABD176EBC4%27)
but the response of json is null {"odata.metadata":"/FalconCPDataService.svc/$metadata#DEPhysicians&$select=FullName,DEPatientVisits/Diagnosis,DEPatientVisits/VisitDate","value":[]}