That is the only message?
Go to help->system info and check the permission tab. If there is something in red, you must change the folder permissions. If you can use FTP, you can set this thing in the backend of joomla and then you should not have any problems.
Hi again! I'm sorry about the permission thing, but as I saw failed to move file the first thing I thought about was file permissions.
We are not ready yet with a native version for 1.5 . That is why you should turn on legacy to have !jocomment.
Please not that legacy is nothing bad You site should be up to 20% slower in some cases with legacy mode on.
Well, if you turn legacy on. All the functions that are for 1.0 will be pointed to the appropriate functions in 1.5. That's all (because this mapping takes place, joomla is a little bit slower, but as I said not more than 20%)
and because !jocomment 3 is written for 1.0 we need the legacy mode.