cannot update value - LINQ

I want update a property in a table (i' am using MS SQL server database) , but it get this error
" THIS PROPERTY IS READONLY"

how do i fix this?

also when I declare  a new linq database instance,
Dim Db As New SageEMSArchiveDataContext
I only get 4 overidable properties (normally this is 5)

I have
import  system.linq

I have checked my references, also stangely another project(on my system) does not have this issue.

any idea why this happens?

Dim Db As New SageEMSArchiveDataContext("Data Source=ADELN250;Initial Catalog=SageEMS;Integrated Security=True")
 
        Dim tbFile = (From files In Db.tbFiles _
                   Select files.Filename, files.ArchiveLocation Where Filename = fName).ToList(0)
 
        If Not tbFile Is Nothing Then
            tbFile.ArchiveLocation = "asdf" 'AT THIS POINT I GET AN ERROR SAYING THAT THIS PROPERTY IS READONLY
        End If

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