Jenkins: 1:523, PostBuild: 1.8

I have a Groovy script . . . that will eventually be a post build script . . . for now the script runs on its own and connects to a Database, but with this CLASSPATH set:

SET CLASSPATH=C:\Users\fmerrow\Downloads\Microsoft JDBC Driver 4.0 for SQL Server\sqljdbc_4.0\enu\sqljdbc4.jar

However, when I try to get the working script to run as a post build . . . I cannot find the class in that file.

I've tried to specify as Directory using "Additional groovy classpath" and when that didn't work as full path to the Jar file. I also wondered if spaces would be an issue . . . Quoting gave odd results (pretended C:\Program Files(x85)\Jenkins to the path) so I moved it into a directory with no spaces (again tried both file and directory) . . . I cannot seem to get it to find the class in this jar file.

Works fine "in the clear" with CLASSPATH set, but I cannot get it to work inside the Jenkins JVM.

Frank