Michael,
Mark is correct about just typing the name of the process on its own action line, so the following is just informational.
The reason you are getting the error:
rule '' uses business object 'p_ReadCurrentLocation' which has not bee found.
is because you are using START PROCESS incorrectly.
with START PROCESS, you provide a Business object and attribute (eg SomeBO.Attr) that contains the name of the process to run.