So normally if you move houses and switch internet providers that should not prevent you from attaching files to an EndNote library.
I would first see if you can attach a pdf files to the Sample Library which is located in Applications\EndNote\Examples.
We have seen issues in the past where the Layout option of the library preventing a file from being attached. So you might try adjust that setting in the Upper Right of the library window to something like Reference Only then try to attach a file and see if you have the same issue or not.
Another option might be to try to drag and drop the pdf to the reference as a way to attach it to see if that change the behavior.
If all these options fail then I would contact Technical Support.
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