We discuss various problems with attribute errors.
If you get an error that specifies the "__of__" attribute, especially when starting, stopping, or installing a ZP, it could be related to misfit objects in the ZODB.
AttributeErrors on the __of__ attribute almost always are an indication that there's an object in ZODB (of class DatabaseMonitorDataSource in this case) for which there's no longer a Python class file for in the expected place in the file system.
The ZenPack appears to have that module/class. Something is out-of-sorts with the ZenPack. When this happens you can install the ZenPack twice, then remove it. The reason to install twice is that oftentimes the first time will fail, but it at least copies the code to the right place that allows the second installation to work.
If that fails you may have to use heavier methods like zenwipe.sh