Hmm no one answereds o I'll give you a few common sense tips.
Something is interrupting the stream of data from your server, usual suspects are your firewall or your router, also incompatible versions (you say they are fine though but this is the most likely cause ie. connecting to a 3.1.2 server with your tekkit set to an older version), you need to trouble shoot a bit.
To troubleshoot, try connecting to a public tekkit server, do you get the same issue? if so then it's a client issue, if it's fine then it's likely to be the server, try rebooting your PC and opening ports for your server in your firewall and router if you have one, also anti virus may block certain activity so disable real time guards to test if this is so, if all fails try a complete fresh install of your server and see if the same issue occurs.