I know this will not be helpful to you, but at least you did not have the whole project failing to load because of a plug-in... In my case a reset (Ctrl+Sh+open) did not help.

Maybe you just need to bite the bullet and do it anyway.

Or maybe you just save the project as is, if you can open it, try a whole reinstall of Vegas (also that did nothing for me) and maybe you're in luck.

Or maybe someone else more knowledgeable here will present a proper solution.

Before you open up your project, with a blank vegas interface, try refreshing the vst effects tab in Preferences. Restart Vegas and then open up your project, and see if that helps.

Why even bother with that particular plug. There are many good free comp/limiter plug-ins available. Kjaerhus Audio has easy to use dynamic processors, The 'Classic Limiter' for instance has just one parameter to set (threshold). Jeroen Breebaart's free 'Broadcast Compressor' offers decent sounding AGC, multi-band compressor and output limiting.  Other favorite dynamic freebes are the simple to use LoudMax and TDR's 'No 6 limiter', which is exceptional but maybe too complicated for non-audio folks with five stages of gain control. All the above work splendidly in VP.

@alifftudm95

eFX Compressor is a Magix plugin that comes with various programs like Samplitude and Soundforge. As far as I know, they are specific to the program that they came with and cannot be used in another program, even a Magix program, unless you purchase the full version separately (essentialFX Suite).

Did eFX Compressor come with Vegas, another Magix product, or did you purchase it separately?

If it did not come with Vegas, then it may have been added in the VST plugins path. You should not try to use it.

Did you try to use it in Vegas and that is why it showed up with an error?

To elaborate on John's comment, confirm the eFX VST folder is selected in the VST default or alternate search folders: (Options> Preferences> VST Effects). I recall the eFX VST <dll> files are somewhere in the Programs files (x86) folder.

As I eluded to in a previous comment, I personally do not like the UI or the sound of the eFX comps, but whatever floats your boat.

I find efX in ...\Vegas Pro 17\MAGIX Plugins\essentialFX\x64\, so Yes, it came with Vegas Pro and not a separate purchase.

Why even bother with that particular plug. There are many good free comp/limiter plug-ins available. Kjaerhus Audio has easy to use dynamic processors, The 'Classic Limiter' for instance has just one parameter to set (threshold). Jeroen Breebaart's free 'Broadcast Compressor' offers decent sounding AGC, multi-band compressor and output limiting.  Other favorite dynamic freebes are the simple to use LoudMax and TDR's 'No 6 limiter', which is exceptional but maybe too complicated for non-audio folks with five stages of gain control. All the above work splendidly in VP.

Thanks so much for those suggestions. The Classic Master Limiter was a little hard to find but is archived here:
https://www.softpedia.com/get/Multimedia/Audio/Audio-Plugins/Classic-Master-Limiter.shtml#download

I found the Jeroen Breebaart's free 'Broadcast Compressor' here:
http://www.vst4free.com/free_vst.php?plugin=Broadcast&id=548

@alifftudm95

eFX Compressor is a Magix plugin that comes with various programs like Samplitude and Soundforge. As far as I know, they are specific to the program that they came with and cannot be used in another program, even a Magix program, unless you purchase the full version separately (essentialFX Suite).

Did eFX Compressor come with Vegas, another Magix product, or did you purchase it separately?

If it did not come with Vegas, then it may have been added in the VST plugins path. You should not try to use it.

Did you try to use it in Vegas and that is why it showed up with an error?

This plug come along with VEGAS. But I manage to resolve my problem.

@alifftudm95

For the benefit of others, how did you resolve your problem?