This is a pretty common error message and can be due to a number of things. First, some plugins really are defective. You’ll see that a lot with foreign-made USB motion controllers. The first thing you should do is make sure you have all third-party Anti-Virus software disabled and run Mach3 as an administrator. If your plugins aren’t actually defective and it was simply a permissions issue, this will take care of it.
If you have another motion controller or another plugin that you have added to your installation, you will need to remove that DLL from the Plugins subfolder in your Mach3 directory. You don’t need to delete it, just drag and drop the file on their desktop or somewhere else in yyour computer where it can be easily located. Then, load Mach3 as Administrator. If it loads without issue, you now know which file was the cause. You will need to find a different or updated version of their plugin.
If it is unclear which plugin is causing the error message, then it’s time for some trial and error. You will need to move one plugin out of the plugin folder, then load Mach3 as Administrator. If the error message appears, then replace that file and remove the next one on the list. Continue this until the error message no longer appears. The file that is NOT in the Plugins folder at that time is the culprit.