I have had the same problem when we migrated from 2007 to 2010.
The problem was that the Parentcolumn was not found on the page, but I could clearly see it.
My dropdown box was a "required" one and I had to rename the Parentcolumn from "Project number" to "Project number Required Field".
On the page the name is still Project number, but it only worked when I added the "Required Field" addition to the name.
Hope this helps someone...
pMzQ,
The problem was that the Parentcolumn was not found on the page, but I could clearly see it.
My dropdown box was a "required" one and I had to rename the Parentcolumn from "Project number" to "Project number Required Field".
On the page the name is still Project number, but it only worked when I added the "Required Field" addition to the name.
Hope this helps someone...
pMzQ,