Comparing Two Major Workbooks By Two Columns and many Params - vba

Question

I'm writing a code to compare two rows in two different workbooks that can be located at different places among the column. The first column is usually grouped (multiple of the same value) in one section. This is why In this code I search by the first column, then pick the other identifier column and offset one at a time while both workbook sheets match each other
I am trying to activate the cell that I find via the .Find function in this code, but apparently you can't do that. "Active method of range class failed"
I believe that I am on the right track with this code, but I'm sure there are still issues, I'm trying to solve one problem at a time with my limited skills!
Thanks for the help :)
Sub Compare2()
Dim layer As String
Dim Pno As String
Dim firstAddress As String
Dim i As Long
Dim c As Range
Option Explicit
For i = 5 To 1000 Step 1
layer = Sheets("MP Parameters").Range("A" & i).Value
Pno = Sheets("MP Parameters").Range("H" & i).Value
With Sheets("Compare").Range("a1:a1500")
Set c = .Find(layer, LookIn:=xlValues)
If Not c Is Nothing Then
firstAddress = c.Address
c.Activate
Do
Sheets("Compare").ActiveCell.Offset(rowOffset:=0, columnOffset:=7).Activate
If Sheets("Compare").ActiveCell = Pno Then
Sheets("Compare").ActiveCell.Offset(rowOffset:=0, columnOffset:=9).Activate
If Sheets("Compare").ActiveCell.Value <> Sheets("MP Parameters").Range("P" & i).Value Then
Sheets("MP Parameters").Range("P" & i).Interior.ColorIndex = 46
End If
End If
Set c = .FindNext(c)
Loop While Not c Is Nothing And c.Address <> firstAddress
i = i + 1
End If
End With
Next i
End Sub

Answer 1

You can only Activate a cell if it's on the ActiveSheet. Since your code references then Activates cells on different sheets, you will cause errors.
You have two options.
Either activate the appropriate sheet first:
Sheet1.Activate
Range("A2").Activate
Or, don't activate a sheet to do a conditional check. You don't have to activate a cell to determine what it's value is. As an example, if you wanted to check what value is in sheet1, cell B2 (irrespective of which sheet is active in the workbook):
If Sheet1.Range("B2").Value = "Yes" ...

Answer 2

The code within your If Not c Is Nothing ... End If block can be changed to:
firstAddress = c.Address
Do
If c.Offset(0, 7).Value = Pno Then
If c.Offset(0, 16).Value <> Sheets("MP Parameters").Range("P" & i).Value Then
Sheets("MP Parameters").Range("P" & i).Interior.ColorIndex = 46
End If
End If
Set c = .FindNext(c)
Loop While Not c Is Nothing And c.Address <> firstAddress
i = i + 1
(I'm not sure what the i = i + 1 is meant to be doing. I've always found it dangerous to modify the loop counter manually. But I left it there as hopefully it is doing what you want it to do.)