If you have very large B machines, the following tips can be useful. Indeed, when you have very large B machines with hundreds of thousands or millions of lines of code, the parsing and loading process can become a bottleneck.
When ProB loads a B machine, it first checks if an up-to-date .prob file is available. To be up-to-date the file must be newer than the main B file and all subsidiary files, and the parser version used to produce the .prob file must match the current version. In case the file is not up-to-date, a Java parser (included as probcliparser.jar in the lib folder) will be used to generate a fresh .prob file.
You can find out the parser version by using