Schema conflicts can occur when two different schemas are introduced in the same session.
Schemas are data structures defined by an add ins for storing data in the model or family's extensible storage. Schemas should have unique IDs. When a schema does not have a unique ID a schema conflict is introduced. This issue generally occurs only when a vendor reuses software code and ID in an add-in. Revit is not able to run when duplicate schemas are present. In order to continue the data from one schema or another must be removed. If you are using an add-in that requires this data is may cause unexpected behavior or cause the add-in to not function. See below for solutions you can use to resolve schema conflicts. The solution may be different based on the context of when you receive a conflicting schema warning.