VBA Loop Macro Fix for search code

I've a problem with some code, I think this is running on an eternal loop but can't figure this out. Please can someone have a look at let me know what they think the problem is. It's a simple lookup and loop code but I seem to have got it wrong. I've now been staring at it for the past two days and I'm flying the white flag.

Sub StoreNumbers()


Dim FoundCell As Range
Dim lastCell As Range
Dim FirstAddr As String
Dim a As Range 'List of stores
Dim b As Range 'List of store numbers
Dim c As Range 'Conversation headers



For Each a In Worksheets("Reference").Range("L2:L1000")

Set c = Sheets("Recieved").Range("C2:C1000")
Set lastCell = c.Cells(c.Cells.Count)
Set FoundCell = c.Find(what:=a, after:=lastCell, LookIn:=xlValues, lookat:=xlPart, searchorder:=xlByRows, _
searchdirection:=xlNext)

If Not FoundCell Is Nothing Then
FirstAddr = FoundCell.Address
Do
Set FoundCell = c.FindNext(FoundCell)

FoundCell.Offset(0, 12).Value = a

Loop Until FoundCell.Address = FirstAddr
End If

Next



End Sub

Thanks in advance

With

Set lastCell = c.Cells(c.Cells.Count)

It should allow the the code to figure out how long it needs to be. I orignally thought this may have been the issue as well but this column is simply text based so there's no forumlae to interfer with this count. I'll have a play about with your suggestion and will let you know the outcome.

---------- Post added at 12:44 PM ---------- Previous post was at 12:37 PM ----------

Ok, I've tried your suggestion and now I'm facing a mismatch error. I've made the *after* section into a range. This is the last cell of the column which is being searched. I really can't see what is going wrong with this

Sub StoreNumbers()


Dim FoundCell As Range
Dim lastCell As Range
Dim FirstAddr As String
Dim a As Range 'List of stores
Dim b As Range 'List of store numbers
Dim c As Range 'Conversation headers



For Each a In Worksheets("Reference").Range("L2:L1000")

Set c = Sheets("Recieved").Range("C2:C1000")
Set lastCell = Sheets("Recieved").Range("C1000")
Set FoundCell = c.Find(what:=a, after:=lastCell, LookIn:=xlValues, lookat:=xlPart, searchorder:=xlByRows, _
searchdirection:=xlNext)

If Not FoundCell Is Nothing Then
FirstAddr = FoundCell.Address
Do
Set FoundCell = c.FindNext(FoundCell)

FoundCell.Offset(0, 12).Value = a

Loop Until FoundCell.Address = FirstAddr
End If

Next



End Sub

Any ideas?