Error 453, Can't find DLL entry point Sleep in kernel32 with VBA call in Office add-in

I have an Office VBA add-in that's causing a problem with one issolated user amongst many others that are not experiencing the the same issue. I've issolated it to the Windows API Sleep function.

This is the declaration I'm using, the 64 bit version coming from official Microsoft documentation (I also tried LongLong instead of Long):

#If VBA6 Then
  ' from Microsoft's Win32API_PtrSage.txt
  Private Declare PtrSafe Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long)
#Else
  Private Declare Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long)
#End If

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When trying to call this with this example in the same module:

Public Sub TestSleep()
    Sleep 1000
End Sub

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This particular user sees this error message:

"453 Can't find DLL entry point Sleep in kernel32"

They are using Office 2016, 32 bit (build 10730) on Windows 10, 64 bit and I have had them check the version of the kernel32.dll which is 10.0.16299.1029, 3/6/2019 (my PC has 10.0.1734.648, 06/03/2019)

What can I do now to establish the cause of the issue and fix it?