The main cause for "Maximum Request Length Execceded" errors is when there's an Incident collection on an object, normally the Group object. The attached script will scan the database for any instances of this collection and tell you which object its on.
Execute the script against your database, it will return a table listing the objects that have an Incident collection on.
Open the System.Group object within Object Designer and remove the invalid collections on this object. Likely candidates would be Incident Collection, Change Collection and Call Collection.
If when trying to remove the collections you receive the error "Error on saving changes: The DELETE statement conflicted with the REFERENCE constraint "fkey$ui_form_item$att".. " this means the collections are on a window and must be removed from there first. The windows to check are Company, Customer, Group, Supplier and Support Group.