I suspect that the error is self explanatory. The styleset (non standard) is available in the document in which it worked but is not available in the other documents in which it doesn't.
Frankly I wouldn't personally use style sets for this. I would create the style(s) that I wanted in a template (or document), then use the function to copy the style(s) from the template/document to the document under process (oDoc), apply the style(s) to the range(s) (oRng) as required and then reset the range to show the style settings that you have applied.
This code below is for one style, but you can sequentially copy other named styles similarly and move the range to its new location before applying them.
Code:
Dim oSource As Document
Const strStyle As String = "AsideStyle" 'The style to copy
'open the template with the styles to be copied to the document
Set oSource = Documents.Open _
(FileName:="C:\Path\TemplateName.dot", _
Visible:=False)
Application.OrganizerCopy Source:= _
oSource.FullName, Destination:= _
oDoc, _
Name:=strStyle, _
Object:=wdOrganizerObjectStyles
With oRng 'apply the style to the range
.Style = strStyle
.Font.Reset
.ParagraphFormat.Reset
End With