The author of VAICOM PRO
has confirmed that VAICOM PRO has compatibility issues with DCS 2.5.6, and is looking into it.
DCS 2.5.6 is currently an open beta release, so issues are to be expected.
VAICOM PRO's support page lists
the thread on the Eagle Dynamics forums, and an email address, through which you can contact them if necessary.
If you would like to disable this plugin for the time being (as it can apparently cause issues with DCS starting, as soon as the plugin has been loaded):
You can disable the VAICOM PRO plugin specifically by unchecking it in the "Plugin Manager", which can be opened using the "Plugin Manager" button on the "General" tab of the VoiceAttack options window, and restarting VoiceAttack.
Or, you can disable plugin support in general (thereby disabling
all plugins you may be using) by unchecking the "Enable Plugin Support" option on the "General" tab of the VoiceAttack options window and restarting VoiceAttack.