sql-server-2008 - Subquery returned more than 1 value in insert statement

Question

I need solution to fix this error Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression. I don't have subquery in my insert statement but still I am getting this error.

Code:

INSERT INTO enquiries_dtls(confdate,confname,region,enquiry,attendedby,dctname,
                           hospital,contactno,email,addr)
VALUES('10/04/2013',
       'APAO',
       'Delhi',
       'test',
       'test',
       'test',
       'test',
       '123214',
       'abc@abc.com',
       'test')

DDL:

CREATE TABLE [dbo].[enquiries_dtls]
(
  [sno] [int] IDENTITY(1,1) NOT NULL, 
  [Timestamp] [timestamp] NULL,
  [confdate] [date] NULL,
  [confname] [varchar](max) NULL, 
  [region] [varchar](50) NULL,
  [enquiry] [varchar](max) NULL,
  [attendedby] [varchar](50) NULL,
  [dctname] [varchar](50) NULL,
  [hospital] [varchar](50) NULL,
  [contactno] [int] NULL,
  [email] [varchar](50) NULL,
  [addr] [varchar](max) NULL,
  [stsupdate] [varchar](max) NULL,
  [dtupdate] [date] NULL, 
  [closingdate] [date] NULL,
  [clsedby] [varchar](50) NULL,
  [revenue] [varchar](50) NULL,
  [apprstatus] [varchar](50) NULL,
  [clsed] [varchar](50) NULL,
  [enqId] [varchar](50) NULL
);