I am trying to update value of codename field on Campaign entity but it wont let me do. In C# code if I debug, I can see it goes through without any error and saves everything else except codename value.
On CRM form it is read only field and if I try to amend it and change value from 12345 to 12345678 for example it does not save.
Any idea what might be preventing it? When I create a new record I can add any value I like.
Your observations are correct: codename
on Campaign can be set when creating a record but cannot be updated.
This information can be seen in the CRM SDK.
See campaign.codename
in the CRM 4.0 SDK: