I get an error message about exceeding the 150-node limit.

You have an evaluation version of the software; or a full purchased version but have not registered it and obtained an registration code. These versions are locked to allow only 150 nodes to be built. A "node" is a line in the Logic or Command block. If you have purchased a full version license of Corvid, send in your Registration User Code and you will be sent an Activation Code that will unlock the program and allow unlimited numbers of nodes. If you have the evaluation version, it is limited to 150 nodes. If you are using certain student versions, the node limit may be 250 nodes.