Welcome to BlackBerry Forums. Sorry you had to call tech support in order to get useless information. The 507 means that that there is no Operating System on the BlackBerry. Here's what you need to do:
- Download the latest version of the 8700 operating system. Start here ->
https://www.blackberry.com/Downloads...E4F82F9F00E7D4 <- and download the handheld operating system for the 8700.
- Execute the program you just downloaded
- Locate and delete VENDOR.XML on your PC C: drive
- Connect the BB and restart Desktop Manager
It should reload now.