Without seeing your document it is hard to predict why you are having this problem in some docs but not others. Based on the line throwing the code I would assume that the revision is in a 'range' that can't be defined for some reason.
A quick fix and dirty fix would be to tell your macro to ignore errors by adding a line at the top of the code which says
On Error Resume Next
We could ask why a particular range is causing the error. We could step through the code and see which Revision is not able to define a range. Could it be in a header/footer, text box, footnote, endnote for instance? However the problem may be something else entirely...
If the revision is to delete text AND you accept that revision, what exactly do you think would be highlighted? And it is a general problem if you are looping through a collection if you are removing collection items as you go - this is why you might see code that steps backwards through numbered items.
So maybe you need to think about what exactly it is you want the macro to do and we can suggest some alternative code to achieve that aim. Tracked Revisions have a type that could provide guidance eg
Addition = Accept and highlight
Deletion = Reject and show as strikethrough
Format Change = Accept and highlight as another colour
Moved??
Maybe start by trying the code on these threads
https://www.msofficeforums.com/word-...tain-font.html
https://www.msofficeforums.com/word/...-document.html