two lines SQL update statement but got a error

[Gison]

Dear all,
I'm a SQL server beginner....
I want to replace description column by add on my name to every strings.
Does anyone can point out where i wrong in following syntax.
thanks a lot.

==SQL statement =============
update Demo
set description = description+ ' gison'

==Error message =============
Server: Msg 8152, Level 16, State 9, Line 1
String or binary data would be truncated.
The statement has been terminated.
=============== ===========

[debasisdas]

check for field size of description field in the table.

[Gison]

thank you for your idea... I'll try it.
:)