String or binary data truncate

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C#3.5

I tried to insert values less than the field in the table definition but I have a problem Server Error in '/' Application. String or binary data would be truncated. The statement has been terminated.

What I have tried:

CREATE TABLE [dbo].[treg] (
[tid] BIGINT IDENTITY (101, 1) NOT NULL,
[uname] NVARCHAR (35) NOT NULL,
[name] NCHAR (40) NOT NULL,
[mail] NVARCHAR (60) NOT NULL,
[addr] NVARCHAR (MAX) NOT NULL,
[photo] VARCHAR (MAX) NOT NULL,
[phone] NVARCHAR (15) NOT NULL,
[addrproof] VARCHAR (MAX) NOT NULL,
[exp] NCHAR (10) NOT NULL,
[category] CHAR (30) NOT NULL,
PRIMARY KEY CLUSTERED ([tid] ASC)
);