Generic SQL error

I have written a small console application having code to create a new lead in CRM 2011.

Lead newLead = new Lead()
            {
                FirstName="test",
                LastName = "test",                
                EMailAddress1 =  "test@test.com",
                CompanyName = "ABC1"

            };
            proxy.Create(newLead);

This generates an error saying "Generic SQL Error".

When I checked the SQL Profiler, it generates 3 error messages related to my application.

1. EventClass = Exception.

   Description = Error: 2601, Severity: 14, State: 1

2. EventClass = User Error Message.

    Description = Cannot insert duplicate key row in object 'dbo.EmailSearchBase' with unique index 'ndx_for_forward_update'.

3. EventClass = User Error Message.

    Description = The statement has been terminated.

I focused on 2nd error message and disabled Lead duplicate detection rules. But still the error occurs. Also I am able to create records from CRM frontend.

If I remove EmailAddress1 field from the code, then lead is created successfully.

Any ideas please

Thanks

Ajay Chawla