How do you try to troubleshoot this message when it works one day, then does not work the next day on the same computer, with the same user, within the same company, with the same document?

Look for anything that changes (new software installed, Windows Updates, updated network permissions...). 

We've seen that with a mapped drive (using alternate credentials) going to "sleep", where the user intermittently loses permission to a network path.

Thanks.  We have tried everything that is documented on any of the Sage sites or elsewhere.  Definitely falls in the category of "Things that make you go hmmmm......."

if it only happens in 1 company, the most common reasons would be this company has "Use  Lockfile" selected or un-selected different than others (this setting is per company) or as mentioned elsewhere here the path is different for those type of documents and that company than for others and that individual PDF Location is having an issue being accessible at the moment the error occurs.  For the Lockfile setting you can use Datafile Display and Maintenance to check the SY_Company file in MAS_SYSTEM folder and compare the value for UsePDFLockFile$ (typically field 51) for the different companies.  You can run File, PL_AdvancedOptions_ui and select the Lockfile to match other companies.

One other option is a Amyuni Document Converter 600 driver conflict (due to Windows updates or other software installed that uses that driver) which makes the version conflict with Sage 100 and these can be intermittent errors - but not typically linked to one company unless that company just happens to have more printing/Paperless activity than others.  See Knowledgebase articles 103205 Paperless Office Printing prompts manually for PDF Location after Windows Updates installed (and a variety of other errors and situations) and the related article # 111219  Download Amyuni Driver Update for Sage 100 2019, 2020, and 2021.

Thanks DGR.  All of those options have been tried as well.  I also spent 1-1/2 hours on the phone with Sage Support yesterday and still no resolution other than running it in MAS90 mode which is definitely not a long term solution.

hmmm. Running ok in MAS90 mode for ADV/PREM could mean it might be permissions, firewall, or Sage 100 Application Server service or application issue... is the Sage 100 ADV/PREM Application Server service running under a domain account or "local system account"?  (should not be Local System Account).. Does this happen on all workstations?  Do you have the users experiencing the issue set to "Spawn tasks from application server" in user's Preferences in Sage 100 or not?  Finally, if Advanced do you have C/S ODBC printing enabled? 

We are Sage 100 Premium v2021. 

The server service is running under a domain service account with full permissions to the file folder location. 

It happens on at least 4 workstations have not tried all.  

No users are set to "Spawn tasks from application server"

Is it just that one Paperless function for the company, or all (journals, sales orders...)?  If it's just that one company / function, a crash could have left bad data behind somewhere... AP_VendorPDFLog is company specific.

This is not a real active company, but does have GL, AP, and AR.  GL is the only module with the issue shows up in.   All other modules work.

If the module posting DTRs are OK, it could be something in the GL data entry tables interfering with things.  Have you tried to Preview the journal to see if the temp table gets created in tempdb?  Query PL_JournalRegister to ensure there is not a phantom entry for that company / GL to write to a bad path.

GL_SourceJournal - look for a bad Next... value.

GL_SourceJournal - look for a bad Next... value.