VBS scripting
To avoid messageboxes generated by shell command, you can add following directives before the execution of such command.
This could be useful to not halt batch operations such as opening multiple files.
okErrorMessages = 0
<invoke DBWShell>
okErrorMessages = 1
.NET scripting
.NET DBWShell implementation is based on the
option General → More...→ 
Execute scripts with no Message Boxes but writing %TMP%/DBWMSG.MSG instead
so the only way to silent the messaging is enabling the option before executing the DBWShell command and then restoring its original state if necessary after the execution.