TeamCity Symbol Server plugin page showed url to be used
http://ourserver/app/symbols/
The fix was to remove the trailing slash
http:
Clicking this URL gives 404, but this is a format that works for Visual Studio 2012 and when trying to validate characters through symchk.exe
eg:
symchk /r mylibrary.dll /s SRV*http://outserver.acp.net/app/symbols
Using this URL, it displays a basic login prompt and the characters load correctly
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