Having sorted out the problem with the autoloader, we can now add the tapes in and it displays them on the screen - it shows the barcodes on the label attached to the tape to help keep them ornganised as well which is quite useful. However, one small issue - 2 of the tapes are marked as "suspect". This is strange; they are both new and have only been used for a basic test.
It turns out that this is a known problem and there is a fairly simple solution. Details can be found here http://technet.microsoft.com/en-us/library/bb808923.aspx. It's to do with the database used by the software - it marks the tapes with data and this can get conflicted if the data and the label don't quite match. It appears that this is what has happened to us as the tapes were used for the testing, before the bar code label was put on.
A couple of caveats for this process; there is a script that you should download and add to a text file to run as a command. Make sure that the script is all on a single line - if it isn't, then the script fails. You might also need to watch what AV solution you use as some don't like you running command files.
It is also important that you follow the described process; remove all suspect tapes, run the script, then add just one of them and run the script again. Then after it detects the tape correctly, erase the data on the tape. Repeat until all tapes are added and data erased. If a tape failes, take it out and add it to the end of the line and use one of the others, until all tapes are OK.
It took a while to complete the process - nearly a full day, but we got there in the end. So all is well....
Well not quite. Now the reporting services function doesn't work. Again, it's known problem, but most of the sites that offer fixes for this, only do so for Server 2008 and we are on 2003. Still, I have hopes that we will get a fix for this fairly soon.
Decided to edit this rather than post a new item having spent a few days working with the guys at Dell. Really helpful chap called Javier who is a SQL specialist - he determined that the reports ran OK through a separate browser window, but not through the DPM console. From this, it appeared to be an issue with the .ASP settings and he did eventually get it fixed. Unfortunately, he didn't give me the exact details as he was working on it using a webex session for several hours. However, from what he told me, there are some issues with access rights - it's probable that the update carried out earlier reset those, which is why it wouldn't run.