Changing prefix of sheet

[Thomas_Mahon]

It may be caused by the scenario described here:

Read-only parameters at random?

This usually happens because you are renumbering sheets with numbers that already exist in your document. Another cause is this problem: 1. Renumber set of sheets A, 2. One of the new numbers exist in the set A, but it doesnt matter since you are renumbering all of them anyway, 3. Process in Dynamo begins, but renumbers a sheet while one of the other sheets in Set A has the same number (i.e. this sheet needs to be renumbered first to ‘free-up’ the number) otherwise the process fails and you get…

If that is the case…then try using Bimorph.RenumberOrRenameSheet as it’s more robust