Adding multiple constraints
The problem is with the erp.table, you are defining primary keys multiple times.

Try the following code:

CREATE TABLE [erp].[table](
    [SysRevID] [timestamp] NOT NULL,
    [SysRowID] [uniqueidentifier] ROWGUIDCOL  NOT NULL DEFAULT (CONVERT([uniqueidentifier],CONVERT([binary](10),newid(),(0))+CONVERT([binary](6),getutcdate(),(0)),(0))),
    [Company] [nvarchar] (8) NOT NULL DEFAULT (''),
    --THE ABOVE ARE DEFAULT FIELDS.  LEAVE THEM ALONE.  ADD FIELDS BELOW
    [AffilationNum] [int] NOT NULL DEFAULT ((0)),
    [VendorNum] [int] NOT NULL ,
    [CreationClass]   [nvarchar] (10),
    FOREIGN KEY ( VendorNum ) REFERENCES Vendor (VendorNum),
CONSTRAINT [idxEvAffiliation] PRIMARY KEY CLUSTERED 
(   [Company] ASC,
    [AffilationNum] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = OFF) ON [PRIMARY]
) ON [PRIMARY]


Refer to Primary Key Constraints and Composite Primary Keys.