<https://easyeda.com/Doc/Tutorial/introduction.htm#PrefixConflictError> Do you mean this? You really need to check <https://easyeda.com/Doc/Tutorial/> out.

To explain a little more: **If:** you have two copies of the same schematic in the same project folder, CctA and Copy_of_CctA. The component prefixes (reference designators or 'tags' as you call them) will be the same in both CctA and Copy_of_CctA. **Or:** you have two different schematics in the same project folder, CctA and CctB but there are some components in CctB that have the same prefixes as in CctA. **Then:** if you try to run a simulation using > **Green Man > Run the Project** then *EasyEDA will try to merge all the schematics in the Project into a single schematic and then run a simulation on that big schematic*. This will fail because it will find repeated instances of components with the same prefix. **Else:** if you try to run a simulation using: > **Green Man > Run the Document** then EasyEDA will run a simulation *only on the schematic in the current active tab in the editor window* (if you have only one schematic open then it will run that one but if you have more than one schematic open then it will run only the one with the selected tab). If you have given a unique prefix to every component in that selected sheet then this simulation will run because EasyEDA will find only single instances of every component in the schematic.