This might sound harsh, but that is something you have to deal with in life (academia or non-academia). What you were tasked to do is present your work so other

This might sound harsh, but that is something you have to deal with in life (academia or non-academia). What you were tasked to do is present your work so other people made room im their calendars to listen to your talk. Finding an error is no reason/excuse not to present your work. BUT you have to make it clear upfront that there is a problem which might invalidate the results. And maybe already give an estimate how far reaching this error is. If you have been working 18 months on a topic you will have substantial knowledge you can communicate to your peers and often some work inspires other work even if they are not using your findings.