I am attempting to analyze a simple assembly in Mechanica and received the following message: "No contacting surface pair could be automatically detected for the creation of separation stiffness. The contacting surfaces will be treated according to the assembly interface defaults or explicitly defined interfaces. If interface bonded, you will need to simplify the geometry of the fastener holes to enable auto selection or explicitly define a contact/free interface in order to keep the two fastened components from being bonded. No separation stiffness will be added." I was able to click OK and proceed, but the analysis fails due to the fastener errors. The most confusing part is that this assembly is symmetric and the opposite side of the assembly where I installed fastener constraints in the same fashion had no issues. Has anyone seen this before and can offer any help? This thread is inactive and closed by the PTC Community Management Team. If you would like to provide a reply and re-open this thread, please notify the moderator and reference the thread. You may also use "Start a topic" button to ask a new question. Please be sure to include what version of the PTC product you are using so another community member knowledgeable about your version may be able to assist.