Upload queue limit reached for your plan
The member has too many pending uploads already — at or above the plan’s batch/queue depth (ul2_max_batch_*). New starts are refused until some finish or cancel.
Why this happens
Same pending-file count as slots, but compared to Max items per upload / queue depth, checked before the parallel slot check. You can hit queue limit even when slot count still looks free if batch ≤ slots. Client-side “only first N files” warnings are the softer cousin when selecting too many at once.
Diagnose and fix
1. Member: finish or cancel pending uploads, then add more.
2. Users & limits → Max items per upload (ul2_max_batch_reg / _prem / _prem_pro). 0 = unlimited (with code caps).
3. Per-user override if needed.
4. Distinguish from File upload slots (parallel) and hourly rate-limit messages.