What version did you last see the backup.syb file and on which OS? Its location moved quite some time ago (when version 9 was still active_ -- maybe it is in a different location now?

Description:

After performing a database backup, a warning message of the form "Unable to open backup log '...'" could be sent to the client and console. Note that this warning comes as a "message" to the client, not as a warning sqlcode from the backup statement. The problem is far more likely to occur on Vista or later when running as a non-elevated process because the server typically tried to write the log into the SQL Anywhere installation directory which is not typically writable by non-elevated processes.

In 9.0.2, 10.0.1, 11.0.0 and 11.0.1, this problem is fixed by properly detecting which of the possible directories for placement of backup.syb are writable and by adding the %ALLUSERSPROFILE%\SQL Anywhere XX (XX=version number) directory to the list of possible directories.

On Vista and later, the %ALLUSERSPROFILE% directory is typically C:\ProgramData. On earlier versions of Windows, it is typically C:\Documents and Settings\All Users\Application Data.