Sarg 2.3.6_2 with squid3 3.1.20 on pfsense 2.1.5
These error-messages like
"Error: Could not find report index file."
"cannot open /usr/local/sarg-reports/yyyy/mm/mm-dd/sarg-date for writing"
were already mentioned in some other sarg threads.
Even in my pfsense system (pfsense 2.15 with squid3 3.1.20 and sarg 2.3.6_2) it occurs unfortunately.
But I have found the following cause:
If the reports are generated multiple times on the same day, then the month-day directories will be generated with an additional sub-index according to the following name pattern "mm-dd.n". But sarg can not open files in these directories because internally it very likely still uses the path without the additional number. If you delete all the mm-day directories of that particular day and re-trigger sarg, it works again – because then sarg does not find any month-day directory and therefore creates the directory without the additional sub-index ...
Since some time at sourceforge is a newer version of sarg available. Perhaps in this release the error is fixed. When will this version be available as pfsense package?