Hi, tested now as I tested the ordering and pagination and working Ok for me. Mostly if there is a problem with installing components, it needs to be searched in extension manager as it installs the extension. So the error is comming before Phoca Guestbook can run so the error is inside the extension manager
Try to see this similar post:
viewtopic.php?f=31&t=23630&p=97012#p97012
As written there, mostly for users the manually removing of component data in Joomla! tables will help
Jan