creation enterprising entities ms crm 4.0

i am perplexing emanate new hit controlling enterprising entity. illustration i found crm sdk code.

// set properties hit controlling ability objects.
        stringproperty firstname = new stringproperty();
        firstname.name = "firstname";
        firstname.value = "jesper";
        stringproperty lastname = new stringproperty();
        lastname.name = "lastname";
        lastname.value = "aaberg";

        // emanate dynamicentity object.
        dynamicentity contactentity = new dynamicentity();

        // set name entity type.
        contactentity.name = entityname.contact.tostring();

        // set properties contact.
        contactentity.properties = new property[] {firstname, lastname};

in formula i have following implementation.

        stringproperty sp_field1 = new stringproperty("field1","value1");
        stringproperty sp_field2 = new stringproperty("field2","value1");

        crmservice use = new crmservice();
        service.credentials = system.net.credentialcache.defaultcredentials;
        // emanate dynamicentity object.
        dynamicentity contactentity = new dynamicentity();
        // set name entity type.
        contactentity.name = entityname.contact.tostring();
        // set properties contact.
        contactentity.properties = new property[] {sp_field1,sp_field2};

i don't many differences code. examples i found internet i have same doing i found sdk. nonetheless i run same i following error

cs0029: can't many modify form 'microsoft.crm.sdk.stringproperty' 'microsoft.crm.sdk.propertycollection'

i attempted combined new non-static form propertycollection(one belongs mscrm namespace) total stringpropertys upheld entity.

microsoft.crm.sdk.propertycollection proptest = new microsoft.crm.sdk.propertycollection();
        proptest.add(sp_ssnno);
        proptest.add(sp_firstname);
        contactentity.properties = new property[] {proptest};

this gave me following error

cs0029: can't many modify form 'microsoft.crm.sdk.propertycollection' 'microsoft.crm.sdk.property'

i am certain the teenager typecasting blunder nonetheless i am means figure out where blunder is. moreover, even typecasting blunder since operative samples given internet me. i attempted removing formula illustration run nonetheless i am encountering same reworking error. greatfully let me know need some-more info this, any assistance appreciated.