Can not find key

Public Sub sele()
If Not IsNull(ThisDrawing.SelectionSets.Item("sel")) Then
Set sset = ThisDrawing.SelectionSets.Item("sel")
sset.Delete
End If
Set sset = ThisDrawing.SelectionSets.Add("sel")
sset.SelectOnScreen
End Sub

These codes are used by other functions.When run above codes,the application have a error "Can not find key".But run below codes,there is OK

Public Sub selsets()
Dim sset As AcadSelectionSet
Dim str As String
Dim selmtxt As AcadMText
Dim getobj As AcadEntity

If Not IsNull(ThisDrawing.SelectionSets.Item("sel")) Then
Set sset = ThisDrawing.SelectionSets.Item("sel")
sset.Delete
End If
Set sset = ThisDrawing.SelectionSets.Add("sel")
sset.SelectOnScreen
For Each getobj In sset
 If getobj.ObjectName Like "*Text" Then
 Set selmtxt = getobj
   
   If selmtxt.TextString = "{\C7;0}" Then 
   selmtxt.TextString = "0.01" 
   selmtxt.Update
   End If
   End If
   Next
End Sub

try Diming the sset inside your version. I think it doesn't know what your trying to do

I have dimed sset by publice dim sset as acadselectionset in the begin of the project,and it's used in other functions.Maybe you are right.I'll try to give sele() a parameter and optimize all sub.

I changed my codes as below

 
Function sele(aa As String) As AcadSelectionSet
Dim sset As AcadSelectionSet
On Error Resume Next 
ThisDrawing.SelectionSets(aa).Delete 
'Don't know the difference between "ThisDrawing.SelectionSets.Item("sel")"
Set sset = ThisDrawing.SelectionSets.Add(aa)
sset.SelectOnScreen
Set sele = sset
End Function