nuDebug Result Error when opening a report

[oli]

I created a report which actually works without any problem.
But evertime the report was created I found following error in nuDebug Result:

[0] :
===USER==========
globeadmin
===PDO MESSAGE===
SQLSTATE[42000]: Syntax error or access violation: 1170 BLOB/TEXT column 'auf_ang_details' used in key specification without a key length
===SQL===========
ALTER TABLE ___nu1607c586f4f4de___ ADD INDEX `auf_ang_details` (`auf_ang_details`)
===BACK TRACE====
C:\wamp64\www\bts-sandbox1\core\nurunpdf.php - line 181 (nuRunQuery)
C:\wamp64\www\bts-sandbox1\core\nurunpdf.php - line 60 (nuBuildReport)

Any idea what this could be - or can I ignore it?
Funny thing is that the field 'auf_ang_details' is not used in the report anymore (but it was before).

[kev1n]

Is auf_ang_details being used as sort criteria?

[oli]

Is auf_ang_details being used as sort criteria?

No, this field is not used as a sort criteria.

[kev1n]

Search the Report JSON for that auf_ang_details

[oli]

I found following entry:
{"sortField":"auf_ang_details","sortBy":"a","sections":[{"id":"","top":110,"height":0,"label":"auf_ang_details Header","page_break":"1","margins":4,"color":"#FFFFFF","objects":[]},{"id":"","top":150,"height":0,"label":"auf_ang_details Footer","page_break":"1","margins":6,"color":"#FFFFFF","objects":[]}

There still was an entry for "auf_ang_details" in Group Properties of the report (don't know how and why) ... I actually never added it there).
After removing it - no more error messages.

Thanks a lot!