Please try:
// get all open excel instances in memory
// btw: GetActiveInstances doesnt use the ROT because some known issues
Excel.Application[] allInstances = Excel.Application.GetActiveInstances();
*Sebastian
// get all open excel instances in memory
// btw: GetActiveInstances doesnt use the ROT because some known issues
Excel.Application[] allInstances = Excel.Application.GetActiveInstances();
*Sebastian