Yes I have seen similar errors on numerous occasions, but I have never seen a 
cause like this one before. I believe the cause is that the SLEs are being run 
against the [[SummaryByMonth]] and [[SummaryByYear]] reports.

The timespan parameter that is used in the SLE signatures is a TimeSpan object 
covering the period of the report. For [[ToDate]] reports this is typically the 
period covered by the current archive record, for example the last 5 minutes. 
However, the [[SummaryByMonth]] and [[SummaryByYear]] reports are generated by 
iterating over all the months and years of data in the archive, so the period 
covered varies as the cheetahgenerator iterates over the months and/or years. 
For example, the January 2014 NOAA report will use a timespan of midnight 1 
January 2014 until midnight 1 February 2014.

The way the SLEs work is that all listed SLEs are evaluated for each report in 
a skin, irrespective of whether they are [[SummaryByMonth]], [[SummaryByYear]] 
or [[ToDate]] reports. So when the January 2014 NOAA report is generated the 
highchartsDay SLE is evaluated using a timespan of midnight 1 January 2014 
until midnight 1 February 2014. Midnight today (24 August 2018) is used as the 
start time and midnight 1 February 2014 is used as the stop time. Consequently 
the error hits.

So why does this affect some people some of the time? The answer is in how the 
[[SummaryByMonth]] and [[SummaryByYear]] reports are generated. Normally only 
the current year and current month reports are generated, these will not 
produce the error. However, if a user deletes all of the generated 
[[SummaryByMonth]] and [[SummaryByYear]] reports then all of the reports are 
regenerated and the error will bite when a historical report is generated. Same 
for any one with a clean install with data from more than 1 month in their 
archive.

Solutions, well a couple come to mind:

1. Create a second skin to generate the [[SummaryByMonth]] and 
[[SummaryByYear]] reports so you can limit the SLE used.
2. It seems your [[SummaryByMonth]] and [[SummaryByYear]] reports are just the 
NOAA format reports, perhaps the Standard skin versions could be used, but this 
may be more complex.
3. Still thinking of number 3.

Gary

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