Board Thread:Questions and Answers/@comment-90.217.74.246-20121227170022/@comment-5319459-20121227171128

In this instance, it is talking about running out of RAM (Random Access Memory). To increase the amount of RAM allocated to run Tekkit you need to open up the launcher and click "Options" under the "Login" button.

You will then see a drop down box labelled "Memory to allocate", from that, chose a higher amount of RAM (for example 512MB to 1GB).

Then click "OK" and start Tekkit.

Good luck!