Answer: If you are using one of the following "debug" shortcuts to stop and restart the Foxhound engine, try running it again; the previous dbeng11.exe process did not have time to release the foxhound1_debug.txt file before a new dbeng11.exe process tried to open that file:

All Programs - Foxhound1 - Tools - Start Foxhound via Firefox - debug

All Programs - Foxhound1 - Tools - Start Foxhound via IE - debug

C:\ProgramData\RisingRoad\Foxhound1>ECHO OFF
Stopping the Foxhound engine if it is running...
SQL Anywhere Stop Server Utility Version 11.0.1.2276
Starting the Foxhound engine...
SQL Anywhere Start Server In Background Utility Version 11.0.1.2276
DBSPAWN ERROR:  -81
Invalid database server command line
******************************************************************
*** ERROR ********************************************************
*** dbspawn/dbeng11 set ERRORLEVEL = 1
*** To display startup diagnostics,
Press any key to continue . . .
04/23 06:39:58. Can't open Message window log file: foxhound1_debug.txt
Press any key to continue . . .

See also...
Invalid database server command line