You can try opening the file with winrar, otherwise you can try manually re-creating it (there are plenty of guides on this).
Providing the log would be easiest, to get to the log file you can open "Launcher Options" then "Open Logs". Find the most recent log, open it, copy the content and use something like pastebin.com or hastebin.com to paste the contents into, then link that here (this is so nobody has to download a file, which is a potential security threat).
Very rarely files can become corrupt when copy/pasting. Did you verify that the modpack.jar is still valid? Otherwise please provide the Technic log file after attempting to launch the modpack.
