Please help us help you and fill where relevant:
Your LimeSurvey version: LimeSurvey Community Edition
Version 5.3.12+220502
Own server or LimeSurvey hosting: Own Server
Survey theme/template: 
==================
Dear all,

While creating an survey I have encountered an problem on IIS when uploading an Image (401)

After checking the uploaded file (survey/upload/968425/images/logo.jpg), I've discovered that the IIS_IUSRS didnt have any permissions at all on it (despite inhereting from the above directories).

Instead an  "limesurvey" user had all the necessary r/w permissions - unfortunately It seems I cant upload any images here through my browser, it become base64 encoded.

Any Ideas how to fix this ?