SQL Server: Violation of PRIMARY KEY constraint

Question

I'm using Microsoft SQL Server 2012 (version = 11.00.5388) and I'm getting an exception

SQLState :23000, Error Message:
Violation of PRIMARY KEY constraint 'PK__MM_DISK___C9EB385C43CE19EE'.

Cannot insert duplicate key in object 'dbo.MM_DISKDATA' The duplicate key value is (1484539200000, 40020675, 1, 40611)..]

while trying to insert a record into the table MM_DISKDATA even the entries are unique am getting the exception.

Example entries:

insert into MM_DISKDATA 
values('1484539200000','40020675','1','40611','79','79','948','12','-1','-1','-1','-1','-1','-1','-1','-1','-1','-1','-1','-1');

insert into MM_DISKDATA 
values('1484539200000','40020676','1','40611','79','79','948','12','-1','-1','-1','-1','-1','-1','-1','-1','-1','-1','-1','-1');

MM_DISKDATA has first four columns as unique constraint.

Please help with this.