function readOnly(count){ }
Starting November 20, the site will be set to read-only. On December 4, 2023,
forum discussions will move to the Trailblazer Community.
+ Start a Discussion
Paweł WoźniakPaweł Woźniak 

Sending emails with big attachemnts gives error: null. No error in Log.

In my org I have strange problem that users are unable to send emails with big attachemnts > 4MB by Lighning Action on Opportunity.
Salesforce in such case wanrn you that attachemtns will be converted to links and as soon as you agree it ends up with message Check the errors on this page: null.
User-added image
Admin users are abe to send. 
What I have done:
- Granted user all possible permisions with permission set including Modiy All data
- Changed profile to Administrator
- Compared profile settings between user who is able to send and this one
- Setup Libraries as is written in SF documentation
- Catch debug logs with all categories set to finest for this user - log has status success and no errors inside.
- Contacted SF support, but they don't know what is an issue

I ho no more ideas what to change. Have anyone seen such error and can advise what to do?

HTML for error:
<div class="pageLevelErrors" data-aura-rendered-by="4:1777;a">
	<div class="desktop forcePageError" aria-live="assertive" data-aura-rendered-by="3:5374;a" data-aura-class="forcePageError">
		<div class="genericNotification" data-aura-rendered-by="5:5374;a">
			<span class="genericError uiOutputText" data-aura-rendered-by="8:5374;a" data-aura-class="uiOutputText">Überprüfen Sie die Fehler auf dieser Seite.</span>
		<ul class="errorsList" data-aura-rendered-by="9:5374;a">
			<li data-aura-rendered-by="11:5374;a">null</li>
		</ul><!--render facet: 13:5374;a--><!--render facet: 14:5374;a-->