Thanks!
So it look like this:
<?xml version="1.0"?>
<configuration>
<runtime>
<generatePublisherEvidence enabled="false"/>
</runtime>
<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0,Profile=Client"/>
<supportedRuntime version="v2.0.50727" sku="Client"/>
</startup>
</configuration>
When I try to save it, it says: access denied on saving, cause he tries to save under a txt
Worked, had to save it on another place, and then cut-past it back to paint.net folder