"Invalid data has been used to update the list item. The field you are trying to update may be read only" SharePoint disaster.

Today I have spent hour and a half trouble-shooting my simple script that uploads CSV data to SharePoint list. On the line that contained item.Update() call (item object is an instance of SPListItem class), I kept getting "Invalid data has been used to update the list item. The field you are trying to update may be read only".

Well the solution was simple, but it just took me hour and a half to figure it out:

NEVER write data to "LinkTitle" field, it is readonly! Use "Title" field instead.

SPBuiltInFieldId.LinkTitle and SPBuiltInFieldId.Title may be used accordingly.