Hi,
this generally happens if you are registering plug-in in sandbox mode, if you see this behavior even if you are selecting sandbox option and if you are able to register plug in assembly successfully then you can ignore this message.
I have seen this in the past and when after successfully registering if I close plug in registration tool or check after day or two it does not display this text. this message text is nothing to worry about if your plug in is working as per your requirement.
my personal guess (I could be wrong) is that this text indicates you could register this plug in Isolate mode as well but if your plug ins are working okay then I suggest ignore this.
MayankP
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