Cumulus Support

exception message : Integer overflow.

It looks like you have left debug logging turned on for a long period. This eventually causes an 'integer overflow' crash in the third party logging component.

I believe you are correct but I have made sure "Debug Log" is not checked on the configuration drop down. I had the same problem last night. Is there another setting? I scanned the ini files and didn't see "debug" options set. I did notice that entries are still being made in the "diag" folder.
I am periodically reading the Nov15log.txt file using a VS2015 C# Winform program (read only) but that doesn't cause the Status/Error light to change.

The setting in Cumulus.ini is called 'logging' in the [Station] section. It's presumably set to one, you need to set it to zero (while Cumulus is stopped).

logging=0

You can confirm that debug logging is on by looking for the debug.log file, yours will presumably be very large and have lots of entries in it (other than things like 'logging disabled' etc).

There is no "logging" entry in cumulus.ini. I did a text search to make sure after visual inspection. The debug.log last entries (assume it appends) are "0000.000 : **** Logging Disabled". Prior (5+ hours ago) to that I see actual entries in debug.log for the sensors which is why I agreed with your analysis. At this point, the file does not appear to be growing in size but generates a new file with a single "Cumulus debug log" record if the file is deleted (19 bytes and not growing).
By the way, excellent documentation, FAQ and support.
I might be going to a RaspberryPI 2 mod 2 interface with a UDP link to my desktop (ultimately web) applications but I really like the Windows GUI presentation.

Now that you don't have debug logging turned on, and deleted the file, you shouldn't hit the problem again.