There is an incompatibility with Solarwinds TFTP app and our Netscreen boot loader. This results in the error message seen. TFTP from ScreenOS works. That is, performing software upgrades and such through 'save soft' command works. Only the boot loader seems to experience this problem. We normally do not have any TFTP issue with packaged TFTP apps. But we do not guarantee to interoperate with all freeware or non-commercial TFTP apps. Solarwinds is a freeware app. Use a different TFTP app such as 3cdaemon or TFTPd32 which I've tested and seems to be compatible.