First, when working with Vlookup you need to handle errors, such as when Vlookup was unable to find a match, you can use If Not IsError(Application.VLookup(.... to achieve this.
Second, in your case you don't need to use On Error GoTo errorbox:, just use the Vlookup error handling I wrote in the first point.
Third, you can use If Trim(ActiveCell.Value2) <> "" Then to verify there is a valid text or number inside ActiveCell rather than empty spaces.
Fourth, you should avoid using ActiveCell, and use fully qualified object instead.
Last, you want to make sure "Fruit Code.xlsx" workbook is open before using the Vlookup, as suggested by @Tim Williams in the comments above.
Modified Code
Option Explicit
Sub lookuphcpcs()
Dim desc As Variant
Dim SourceWb As Workbook
' error trapping in case Fruit Code workbook is closed
On Error Resume Next
Set SourceWb = Workbooks("Fruit Code.xlsx")
On Error GoTo 0
If SourceWb Is Nothing Then
Set SourceWb = Workbooks.Open("C:\Users\Username\Desktop\Fruit Code.xlsx") ' open workbook if it's closed
End If
If Trim(ActiveCell.Value2) <> "" Then ' make sure cell has a string other than space
If Not IsError(Application.VLookup(ActiveCell.Value2, SourceWb.Sheets("Sheet1").Range("A2:B7"), 2, 0)) Then
desc = Application.VLookup(ActiveCell.Value2, SourceWb.Sheets("Sheet1").Range("A2:B7"), 2, 0)
MsgBox "Description for HCPCS Code " & ActiveCell.Value2 & " is """ & desc & """"
Else
MsgBox "No Description found under HCPCS list!"
Exit Sub
End If
Else
MsgBox "You did not enter any input!"
End If
End Sub
