Dangerous file detected:512
I do not know why magespace is giving you this error. I had never heard of them until I saw your message, and I have no influence on whatever their malicious code detector is doing. I tried to reproduce your problem with them, but they wanted me to pay for an account to repeat the upload you tried. You could try to upload the files from the civitai page instead, though they are exactly the same files there so there's not strong reason to think it would help https://civitai.com/models/87781/boringe621-negative-embedding-enhance-images-stylistically-and-topically .
I guess I would call boring_e621_v4 the most robust version. It should work on the most models. The fluffyrock version is intended for models with "fluffyrock" in their names, as these models were trained in a different way that robs general purpose textual inversion embeddings of some of their efficacy.
On the topic of the word "by", to use the original version of this embedding, I instructed people to write "by boring_e621" in their negative prompts. I noticed when searching for people using it online that they often left the word "by" out, making it less effective. So I trained all of the newer versions (like boring_e621_v4) so that they no longer required you to write "by" before them to use them properly. So the right way to use boring_e621_v4 is to write "boring_e621_v4" in the negative prompt (without quotes or the word "by").