Tekkit 1.2.8c has a Java 1.7 requirement, fix is incoming.

[Skuli]

You can either upgrade your java to 1.7 or wait for 1.2.8d, which I'm hoping to have shortly.

[Andrew2060]

i tried it, but it still crashes me on mojang screen, i have made a topic and a bug report.

i am a mac user and have latest java installed