Once it hits the error on the first folder, it will never error out on it again until the next day.
Sounds like a transient variable value problem IF you're saying this bombs out after n loops. Not clear if you are saying it completely runs once n times, then on another run attempt it will fail OR you are saying you call this once, it loops n times then typically fails at the same point. I'll answer as if it is the latter.
Next time you run it, start from square 1 by putting a break at the beginning. Since the point of failure seems to be known, either step through to just before that point or allow it to loop until just before that point. If that is after a lot of loops, then I have dealt with this by adding a counter and just holding down F8 to repeatedly loop and periodically checking progress, switching back to slow advance when I get close. The goal is to compare the state of variables, so the watch window will be useful. I don't believe I've tried to construct an IF block where execution branches to when counter reaches a value where that block also has a break point but that may also serve to interrupt at the proper number of loops.
There are other issues with your code. #1 - please use code tags with indentation (# on menu bar) otherwise large blocks are difficult to read. There are other reasons as well.
Also, omitting the code parts that tell us that a variable is declared or properly typed doesn't help. It is also not evident that you are using Option Explicit. Code comments explaining the intent would help. For instance, I do not understand your use of the Replace function - looking for a zero length string in a folder path, replacing it with vbNullString, which AFAIK, will be treated the same here. Thus aside from replacing what is essentially a zls with a zls, how could a file path contain a zls in the first place? Maybe there is something there that I could learn?
Then there is the expectation that I have that if Count <> 10 nothing gets executed between that line and iFileNumber = FreeFile. Does whatever comes after that have all the variables set up correctly? I expect that Drive, Server, etc. are Null in that case.
You said that the error occurs on For Each Subfolder In FOLDER.SubFolders but didn't show what comes before that.
If none of that helps, try posting the entire procedure (in code tags) and indicate the status of Option Explicit. However, what seems most problematic for me is what happens if Count does not equal 10. If I missed an End If on that, it proves my point about not being able to accurately read code as general post text.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.