dll without visible references "Can't add a reference to the specified file"

I am writing a dll which uses methods to calculate certain variables.
This dll is provided to a software creator who uses this dll in his programms which is then distributed to the public.

Now my problem, the software provider needs to see the functions when using my dll in his software, so I declared them public.
When he distributes the dll with his software I want to avoid that other users use this functions to perform certain calculations is there a way.

I have seen dll which when I try to reference them in VB the message:
Can't add a reference to the specified file
comes up mut I know the dll is used with methods and so on
How can I do the same for my dll
themrocAsked:
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ClifCommented:
You can create a license file which contains an encoded string.  Let your vender know how to decode the string and, when they do, pass it to your dll.  If the decoded password "fits", allow the dll to execute.  If not, throw up a message box informing the unauthorized developer that he needs a license.
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themrocAuthor Commented:
Is there a way to prevent already that the user can see the methods in the object browser with F2

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IanWelchCommented:
"Is there a way to prevent already that the user can see the methods in the object browser with F2"

No, not that I know of.

Another option is to create your component as an invisible user-control and compile it as an OCX. There's an option in Project/Properties to 'Require License Key' and when that's checked VB will create a 'lic' file which must be present in order to use the control at design-time. So you would need to give your customer the OCX and LIC file so that they can add it to their project. Then they just distribute the OCX without the LIC file. Obviously, the drawback to this approach is that the control needs to be added to a form before it can be used.

Unfortunately, that type of functionality isn't available for DLLs so you need to 'Do It Yourself' as Clif suggested.
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themrocAuthor Commented:
thanks for the comments, was not quiet what I expected but did help
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