Jochen,
Shawn's example does work fine, the problem you are having is that the Base64 string is created from a .ico file.

Shawn's example with the correct Base64 string:
Code:
Break On 

$System = CreateObject("Kixforms.System") 

$Form = $System.Form() 
$Form.Text = "Demo" 
$Form.Icon = $System.Icon.FromBase64String(UserIconString()) 

$Form.Center 
$Form.Show 
While $Form.Visible 
 $= Execute($System.Application.DoEvents) 
Loop 

Exit 0 

Function UserIconString() 
$UserIconString = " 
AAABAAEAEBAQAAAAAAAoAQAAFgAAACgAAAAQAAAAIAAAAAEABAAAAAAAwAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAACAAACAAAAAgIAAgAAAAIAAgACAgAAAgICAAMDAwAAAAP8AAP8AAAD/
/wD/AAAA/wD/AP//AAD///8AAAAAAAAAAAAP/////4iP8A////iAAI/wD///AACQj/AP//8I
8AD/8A///wj/iI/wD///CIAAj/AP//8AAKCP8A///wiAAP/w+IiAAI////DwAACwj///8PCP
8AD////w8I////////AACJmZmZmZkA4ImZmZmZmQAAgAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" 
EndFunction
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