What are Error Codes 85, 86 and 90?

These are generic failure messages for the different service provider groups on a Switchvox System.
Error 85 refers to any failed call over SIP.
Error 86 refers to any failed call over IAX.
Error 90 refers to any failed call over a Channel Group (Can be either Analog or PRI/BRI group)

Where can I find the actual cause code?

These errors are usually encountered when placing a call and are played back over the line to the caller.
Once they have been encountered follow the steps below:

Note the time of the call, the code received and the number dialed.
Login to the Switchvox Admin Suite and Navigate to Reporting -> Call Logs
Select an appropriate date range, Choose All Calls for Type and click View Log
Locate your failed call from this listing
Click the 'Actions' button to the right of the failed call
The ISDN Cause code will be listed here, along with the actions which occurred before it was encountered which is often helpful in determining the actual cause.

If the failed call does not show up in the Call Log, another method can be used to troubleshoot:

For PRI calls, start a PRI Debug under Server -> Advanced Debugging.
For SIP calls, start a Packet Capture under Server -> Advanced Debugging.
Make the call fail again
Stop the Debug or Capture and Download

Once a failed call is captured, everything sent and received by the Switchvox can be examined for cause codes and failure messages.