pivot table limitation ?

1500(rows) by 12(columns) original table. I’m trying to create a pivot, one field in columns as soon as I add the 6th in the rows section I get :
“MS Excel cannot create pivot, Too many row or column items”. Microsoft knowledgebase only talks about 32.000 or so column item limitation, or some billion items for rows, so I don’t think it’s the case.
If I split the original table in 4 (about 3-400 rows), it works.

What limitation do I miss ?