Explanation:

If a CALL start_OFSS_monitor() statement fails with "Cannot access file ... Permission denied SQLCODE=-602", and

• you are using UNC file specification like SET unload_path = '\\\\Xps\\c\\DATA\\OFSSremote\\'

• with an OFSS subject database being run as a Windows service,

• try using the dbsvc -a and -p options to create the service to run under the account name and password for a Microsoft Windows account you have created

• instead of using dbsvc -as to run under the Windows LocalSystem account.

For example, if you created the OFSS subject database service with dbsvc -as, you might see the following exception that is raised by an UNLOAD TABLE statement inside the OFSS script:

-- Subject database ISQL session

PARAMETERS OWNER;
UPDATE "{OWNER}".OFSS_settings SET unload_path = '\\\\Xps\\c\\DATA\\OFSSremote\\';
UPDATE "{OWNER}".OFSS_settings SET max_batch_duration = '7m'; 
UPDATE "{OWNER}".OFSS_settings SET encryption_key     = 'KeHX8?k1Rqz/5FvOu{nhx1#mQxy0@95e'; -- the values must agree
UPDATE "{OWNER}".OFSS_settings SET max_batch_size     = '1M'; 
UPDATE "{OWNER}".OFSS_settings SET server_messages_are_to_be_captured = 'Y';
CALL "{OWNER}".start_OFSS_monitor();

Could not execute statement.
Cannot access file
'\\Xps\c\DATA\OFSSremote\OFSS-ddd-batch------2-uuid-3728852...' --
Permission denied
SQLCODE=-602, ODBC 3 State="HY000"
C:\ProgramData\RisingRoad\Foxhound5\scripts\OFSS_1_setup.sql:7
CALL "dba".start_OFSS_monitor()

-- OFSS diagnostic table on the subject database

SELECT * FROM OFSS_exception;

exception_id,inserted_at,diagnostic_text
1,2019-07-29 16:35:00.924,OFSS-b2e(OFSSehb2) SQLCODE = -602, SQLSTATE = WL002, 
   ERRORMSG() = Cannot access file '\\\\Xps\\c\\DATA\\OFSSremote\\OFSS-arbiter-batch------2-uuid-dfa...' -- Permission denied

Here's a template for using the dbsvc -a and -p options to set up a High Availability partner database as a service:

"%SQLANY17%\Bin64\dbsvc.exe"^
  -a youraccount^
  -o "xxx\dbsvc_partner1_log.txt"^
  -p yourpassword^
  -s Automatic^
  -sd "SQL Anywhere 17 Partner1 Server"^
  -sn nnnnnnnn^
  -t Network^
  -y^
  -w nnnnnnnn^
  "%SQLANY17%\bin64\dbsrv17.exe"^
  -dt "ttt"^
  -n nnnnnnnn^
  -o "yyy\dbsrv17_partner1_log.txt"^
  -oe "yyy\dbsrv17_partner1_startup_log.txt"^
  -su sqlsql^
  -x tcpip(port=99999;dobroadcast=no)^
  -zp^
  -zl^
  -zt^
  "zzz\ddd.db"^
  -xp on