I just upgraded a site from 6.1.5 to 7.06, but had a lot of trouble. here are my notes so that others may not have so much pain maybe.

I first tried to go from 615 straight to 706 but got a blank Server Error message. The event logs said something about there being dupe lines in the web config for the .net version I think. I fiddled around with it for a while changing the .net version the app pool was running in between 2.0 and 4.0 hoping it would magically work but it didn't. I knew I was going from 2.0 to 4.0 but wasn't sure who was in charge of making the change - me or the install.

I already have another site running 7.03 so I know the .net 4.0 is ok.

So I decided to go from 615 to 620 like the upgrade path wiki says. Again I got an error, but this one was a little different, didn't seem to have to do with the system.web stuff in the web config. 

1st fix - I found a post on dnncreative about making sure the zip is not blocked:

http://www.dnncreative.com/Forum/tabi...

that fixed my upgrade to 620 - I re-extracted everything over the folder and it upgraded.

Back to upgrading to 706, now from 620. Same error - something about a duplicate in the web config having to do with system.web: An assembly with the same identity ‘System.Web.Extensions or something. i googled that and came up with this magical tidbit:

http://www.interactivewebs.com/blog/i...

I did what it said - add .bak to a dll in the bin file - I assume the .bak part isn't important - just renaming it probably fixes the duplicate. Now it all works.

Phew. I believe the dll could have been changed in my initial upgrade from 615 and it would have worked...

This install has been around for several years, at least since 2007, not sure what version it started on.