Is there existing integration between the Salesforce and Location modules?
It's difficult to say what's the exact problem, but I think you could have unmapped property in your configuration.
So please go to /admin/structure/salesforce/mappings and verify all the objects that have the properly set mappings and the tokens are valid.

If this doesn't help, try the following options:


Clear the cache (including memcached).
Check watchdog logs for further info.
Double check your Salesforce mappings again if you didn't miss anything.
Upgrade your Location and Salesforce module to development version just to test.
Look for any existing issues.
Debug the code using xdebug.
Report the issue or bug report on Drupal site against the right module.


You may also try the following related links:


Location - Select User Primary
Support Salesforce attachment sync