I presume this is a Cisco router ?
As there are many ways for this to fail, you need to post the messages here for the whole process you are trying. Also post the part of the configuration for the interface that is connected to the same subnet as the TFTP server.
There are no passwords, so it should be safe for you to do this. If we can see exactly what is happening, then we can help you further.
If possible, I might recommend using FTP if possible. TFTP has a problem with windowing. Often times, this will cause hiccups and not let them be fixed. FTP is a reliable protocol and much more likely to work for you.