We have found that if some report contains wrong SQL queries stored in the report itself, OR this queries have become invalid later, e.g. if some fields was renamed in the database, then no way to see these errors.
Solution is to add to VSERVER one more standard log file, into which will write info VREPORT.dll.
This log file can be set ON/OFF using same SQL commands as Warning.log file of the Valentina Kernel.