When GAMS cannot write to the .lst file, it assumes that the GAMSIDE is holding the file. To release the, it uses the IDECmds program to send a message to the GAMSIDE. If the GAMSIDE is not running and another program is impeding GAMS to write to the .lst file , you will get that error messages.

*** IDECmds error = GAMSIDE is not running
***
*** IDECmdsRC=2 ViewClose request failed on gams.lst
***
*** Unable to open output file (RC=13) c:\temp\gams.lst
*** SysMsg: Permission denied

When running a mode from the GAMSIDE, the GAMSIDE will close the .lst file itself.