You can explode it via vba.
Code:
Sub ForceExplode()
On Error Resume Next
Dim retBlock As AcadBlockReference
ThisDrawing.Utility.GetEntity retBlock, basePnt, vbCrLf & "Select Non-explodable Block to Explode"
retBlock.Explode
retBlock.Delete
End Sub
If the cause of being unexplodable is just unchecking the "Allow Exploding" option while creating the block, that's easy. But if the reason is varying x,y, and z-scale, its a different story. If the resulting object is valid, then it can be exploded. For example, a circle inside a block is non-uniformly scaled, when exploded will be an ellipse-valid. But a non-uniformly scaled sphere, when exploded will result to a null object and therefore will be deleted. So it depends on the type of objects inside your block.