There is a file limit, I use KiWi Cattools and the tftp transfer only gets to 20971520 and then tanks. I checked the web and there appears to be a 32MB limit. Not sure what that is all about. Looks like it's time to find another TFTP server program......
Given this request was placed in 2007, I'm not sure it's valid to respond to.
If someone still has this issue with TFTP, then it's time to SCP or SFTP. Either of them are able to handle that file size. Both servers are available from SolarWinds' web site.