[SalesForce] Error while running a test class to add a partner to a user group

This is the test class I have Written and every time I run the test I get the following error:

Class               addPartnerUsersToGroupTest
Method Name         TestaddPartnerUsersToGroup
Pass/Fail           Fail
Error Message       System.DmlException: Insert failed. First exception on row 0; first error: INVALID_CROSS_REFERENCE_KEY, Cannot create a portal user without contact: [ContactId]
Stack Trace         Class.addPartnerUsersToGroupTest.TestaddPartnerUsersToGroup: line 26, column 1

For the test class beneath

@isTest (SeeAllData=true)
private class addPartnerUsersToGroupTest{
    public static Account partnerAccount; 
    static testMethod void TestaddPartnerUsersToGroup() {
        partnerAccount = new Account(Name = 'Test Partner Acccount');                                                                           
        insert partnerAccount; 
        Contact partnerContact = new Contact(FirstName = 'Test Contact',LastName = 'Test Contact',
                AccountId = partnerAccount.Id,Email = 'testemail'+Math.round(Math.random()*Math.pow(10, 7))+'@testemail.com');

         String communityNick = Math.round(Math.random()*Math.pow(10, 7))+'';
         Profile p = [Select p.Name, p.Id From Profile p where p.Name =: LABEL.Partner_Distributor];
           // Create Partner Users
         User partnerUser1 = new User();
         partnerUser1.LastName ='Test name';
         partnerUser1.Alias ='tetest';
         partnerUser1.Email ='testemail'+Math.round(Math.random()*Math.pow(10, 7))+'@testemail.com';
         partnerUser1.Username ='testemail'+Math.round(Math.random()*Math.pow(10, 7))+'@testemai.com';
         partnerUser1.CommunityNickname = 'TestCommunityName1'+communityNick.substring(0,4);
         partnerUser1.ProfileId = p.Id;
         partnerUser1.ContactId = partnerContact.Id;
         partnerUser1.TimeZoneSidKey ='Asia/Kolkata';
         partnerUser1.LocaleSidKey ='en_IN';
         partnerUser1.EmailEncodingKey ='UTF-8';
         partnerUser1.LanguageLocaleKey ='en_US';
         partnerUser1.isActive = true;
         insert partnerUser1;
    }    
}