It doesn't make sense to set an item read only if it needs to be modified and opositeThink of a long 20-digit string comprising sub-components. Each component string is familiar to the user so from a data-entry perspective it makes sense to split the field into pieces and ask the user to key in the pieces.
2. remove the read only condition and make the item to be a display only itemAs stated, using a display-only item also raises the same error.
I don’t see any problem when the item is declared as Display Only. See this example:
The use case is there is a Display Only item (or Text item with Readonly condition Always, both of them look the same on the page) which is set using a Set Value DA using a couple of helper fields on the page.