Encoding in UpdatePanel

Today I had a strange error in a web application which was running fine for years. But now Turkish people should start to use that application.

And they had strange problems: The UpdateProgress panel a.k.a “Ajax rolling donut” was not working and in the F12 javascript console I had the following error:

unable to get property ‘length’ of undefined or null reference in ScriptResource.axd, line 2 character 18053

To fix the error I needed to change

<system.web>
  <globalization culture="auto" uiCulture="auto" />
</system.web>

to

<system.web>
  <globalization culture="auto" />
</system.web>

Why should I not set uiCulture? I do not know!