Firstly, try simply closing TRANSYT 12 and then opening it again. This may ‘reset’ the diagram. If this does not work, check the folder(s) where you are saving and loading both the TRANSYT .DAT file and the NetCon .NCE file. You may have saved several copies of the file as you have worked on the file. In this case, take the current .DAT and .NCE files and copy/move them to a new folder. Loading the files from this new location into TRANSYT should solve the problem. (Alternatively, you can delete all the files that you know are unused.)