As users start publishing Visio diagrams, especially data connected diagrams, to Visio Services you may find the need to troubleshoot rendering and refreshing errors.

All Visio Services activities are logged to the trace log.  Where is your trace log?  By default it is located at

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Also, by default, Visio Services is set to a Medium logging level…

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I suggest you change this to Verbose when troubleshooting issues with Visio Services.

To do this, go to Central Administration and click on Monitoring.
In Monitoring select Configure Diagnostic Logging

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In order to change the logging level, select Visio Graphics Service and all the sub items will be selected.
Set the Least Critical Event options both to Verbose

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Click on OK to set these options.

If you go back and check you will see that they are all set to Verbose…

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Now you should be able to see everything using the ULSViewer…

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Notice that all the Visio Services related entries have the Product field set to “Visio Graphics Service”.

NOTE: Make sure to set it back when you are done troubleshooting.