Expectations for Undergraduate Research
Having been, worked with, and supervised a number of undergraduate researchers in my time, a few thoughts:

If people have been working on a problem for years, it means there are pieces of that problem to work on. There is often a perception, I find, with new researchers, that the process of doing research is an on/off switch...that there is nothing...nothing...nothing...BAM! Breakthrough.

For most research, this isn't the case. Particularly good undergraduate projects are pieces of a larger whole, and generally are accomplishable over the course of a summer. Testing a particular hypothesis. Working on the implementation of the algorithm on a new platform/language, etc. Applying existing tools to new data or areas as a proof of concept. Testing the sensitivity of the results of a tool to some of the parameters used for it.

Undergraduate research, to be "successful", should produce a project the undergraduate can take ownership of (i.e. not just "Write the code one of my postdocs can't be bothered to) and helps move the lab's research agenda forward, but it's not necessarily supposed to produce flashy standalone results or major breakthroughs.