I'll take a shot here , there normally is no tftp address on a router you use a router interface or a loopback address for the router . If you are trying to copy the running config to your solarwinds server you can do the following.
At the prompt on the router>
Write net , hit enter , it will ask you for the tftp server (solarwinds address) , enter that and hit enter again and it will ask you for the name of the file on the solarwinds server you want to name it such as router-confg or whatever you choose to name the file. Normally you will have to have the router config file defined on the tftp server beforehand and the correct permissions that will allow you to write it to the file . Of course you will have to make sure you can get to the Solarwinds server , check by pinging the solarwinds address before starting above procedure .