When I get the error it crashes the 'build' in Eclipse and returns an error like:
An internal error occurred during: "Building workspace".
The Spock compiler plugin could not run because Spock 0.5.0-groovy-1.8 is not compatible with Groovy 1.7.10.'
Why is this an 'internal error'? It is a problem with the user's project setup and workspace conf.
Also I think this internal error crashes the build which tends to leave the workspace UI etc. in a confused state leading to other weird problems (such as exceptions being thrown from some UI processes).
It would be nicer when this error rather than 'crashing' the Eclipse build would instead result in some kind of an error marker in the Problems view... it may also help in identifying a project or resource involved in causing the error. (Maybe a specific project / resource that has spock tests in it in this case).