If you are a class user, your class only have access to a limited number of nodes. You can see how many nodes are available for your class on your My DETERlab page.
Something like this:
Admission Control: $project/$experiment has too many nodes allocated!
Each class is limited to a portion of its max required nodes for the duration of an assignment. This portion is around 1/4-1/3 for large classes and around 1/2 for small ones. It is somewhat subjectively set by DETERLab ops team but it can be changed by instructors by modifying the "limit" row for their class in the GoogleDoc spreadsheet.
Collectively all classes will be limited to 2/3 of the maximum capacity of the testbed at all times (which is to say: 265 nodes).
DETERlab has 400 nodes (physical PCs) split between ISI in Marina del Rey and UC Berkeley. They are our most scarce resource.
In order to provide fair access to nodes to all users of the testbed (researchers and classes alike), we impose limits on the maximum number of nodes available to classes.