But if I let the install add it's own SQL Server instance, that works OK.

Hi John - no, 32 bit.  I'm about to try an install on another machine (Win 7). I'l report back.
Alan

Thanks Mike, I was already aware of these issues - but I might not have been!

I will summarise what I have done today:

1) Wondering whether the problem might lie with SQL Server Express 2008 R2, I tried installing R6.15 onto SQL Server Express 2008 "R1".  I tried this on both my XP and Win 7 machines, but with the same "Invalid class string" error.

2) I then decided to try an earlier version of R6 - the only disc I have is 6.10.4 so I tried that (on XP and on SQL Server Express 2008 R2). It's installed without problem.

So the problem seems to be with my 6.15 install disc.

I guess since I want to be done with this I'm going to download all the updates and run them over the 6.10.4 install.

Alan

What would be interesting to know is if, once you have Recorder running under in SQl Server 2005, if you move the database (by detaching and attaching it to your 2008 instance) then change the registry to point  Recorder to the  SQL Server 2008 instance will Recorder continue to work.

Mike

Whew, I'm up and running again, but it was a close call (see below). What I did was:

1) install Recorder (onto XP) opting to install the default SQL Server 2005 database.
2) separately install SQL Server 2008 R2 on the same machine;
3) (in SQL Server Managment Studio) restored my NBNData backup to the 2008 R2 instance;
4) detached the new (empty) NBNData data files from the 2005 instance;
5) in the Registry, pointed Recorder to the 2008 R2 instance.

This worked and so far everything seems to be OK.  The "close call" arose because my misunderstanding of how the SQL Server backups work. I'd opted to backup to two locations, assuming this gave me two identical backup files, either of which could be restored from. In fact, two files are produced which are complementary, and both are required for a database restore. Now, one of the files was on my old laptop, which I'd had to return (a risky strategy in any case you might observe, having only one backup and having deleted the main database, and the backup,  from the old laptop).

I was unable to restore from the single file on my local external hard drive, at which point I started to get seriously worried. Luckily our IT support was able to recover the deleted back up file on the old laptop, and copy it to me. A lesson learned - the hard way.

None of this of course helps to explain the original problem of the "invalid class string" error when trying to install Recorder directly onto the 2008 R2 instance.

Cheers

Alan

Thanks Mike, interesting. I suppose the question arises - are there any significant advantages in using SQL Server 2008 R2 over 2005, or over 2008 "R1". Has anyone looked into this?