Understanding Scan Failures and How to Fix Them
When PaperScorer can’t process a scanned sheet, it marks the upload as failed and shows an error message. This article explains the most common failure reasons and exactly how to fix them.
Where to Find Failed Scans
Go to Upload & Score and look at your upload history. Each row has a status:
- Processing — still being scanned.
- Success — every page in the upload was processed cleanly.
- Completed with errors — at least one page in the upload failed to process.
Click into any upload to see a thumbnail of each page, its status, and the specific reason any failed pages didn’t process.
Common Failure Reasons (and Fixes)
1. Unable to detect QR code / alignment markers
What it means: PaperScorer couldn’t find the QR code or corner alignment markers on the sheet. These are essential for identifying the assessment and student the sheet belongs to.
Most common causes:
- The sheet was printed with “Fit to Page” scaling, shifting the markers.
- The page is cut off, torn, or folded at the corners.
- The scan resolution is too low (below 200 DPI).
- The QR code or a corner marker is covered by a staple, tape, or student writing.
How to fix it:
- Reprint the sheet at 100% / Actual Size, not “Fit to Page.”
- Re-scan at 300 DPI in grayscale.
- Make sure all four corners and the QR code are fully visible and unobstructed.
- If the original sheet is damaged, print a fresh copy and have the student re-bubble.
2. Student identifier could not be read
What it means: PaperScorer found the sheet but couldn’t determine which student it belongs to. This usually means the student-ID bubbles weren’t filled in correctly.
Most common causes:
- Student forgot to bubble in their ID entirely.
- Bubbles are filled too lightly.
- Wrong number of digits bubbled (e.g. 5 digits for an 8-digit ID field).
- Multiple bubbles filled in the same column.
How to fix it:
- Open the assessment and go to its Scan History view, then find the failed sheet and look at the scanned image.
- If you can read the student’s name or ID, use the sheet’s Reassign scanned test action to assign it to the right student.
- For future assessments, print pre-filled class scan sheets — this eliminates the bubble-in-ID step entirely. See Printing an Assessment for a Class.
3. Image quality too low
What it means: the scan is too blurry, dark, or low-resolution for the engine to reliably read bubbles.
Most common causes:
- Scanner DPI set below 200.
- Color mode set to 1-bit black-and-white (loses brightness data the engine needs).
- Mobile phone photo taken in low light or at a sharp angle.
- Aggressive PDF compression after scanning.
How to fix it:
- For document scanners: set DPI to 300, color mode to grayscale (not 1-bit B&W).
- For mobile scans: use bright, even lighting and hold the phone parallel to the sheet. See Mobile App Scanning Guidelines.
- Don’t compress PDFs after scanning — upload the original file.
See Ideal Scanner Settings for the full recommended configuration.
4. Page orientation incorrect
What it means: the sheet was scanned upside down or sideways and the engine couldn’t locate the markers.
Most common causes:
- Sheets were loaded into the scanner in the wrong direction.
- A mix of orientations in a single PDF (some sheets face up, some face down).
How to fix it:
- Most modern scanners have an auto-rotate setting — enable it.
- Before scanning, sort sheets so they’re all oriented the same way.
- If you’ve already uploaded, rotate and re-upload just the failed pages.
5. Sheet damage or stray marks in the bubble area
What it means: folds, creases, smudges, or doodles in the answer-grid area are interfering with detection.
How to fix it:
- Flatten damaged sheets as much as possible before re-scanning.
- If the damage is severe, print a fresh sheet and have the student re-bubble.
- For future assessments, share Testing Guidelines with students — no doodles, no folds, no writing outside response boxes.
6. Engine misread an individual answer
What it means: the sheet processed overall, but a specific question’s answer was read incorrectly (or not at all). This isn’t a hard failure — the student gets a score — but the score may be wrong.
How to fix it:
- Use the manual-correction flow to override the recorded answer or score for that one question. See Changing a Question Answer.
7. Unknown error
What it means: something went wrong that doesn’t match the categories above. Rare, but can happen during temporary service issues.
How to fix it:
- Wait a few minutes and try uploading the sheet again.
- If it fails repeatedly, email support@paperscorer.com with the date and time of the failed upload and a copy of the original scan file.
Prevention Checklist
Before your next scanning session:
- Sheets printed at Actual Size / 100% (not “Fit to Page”)
- Sheets printed on plain Letter (8.5″ × 11″) paper
- Scanner set to 300 DPI, grayscale
- All sheets oriented the same way
- No folds, staples, or tape covering QR codes or corner markers
- Students instructed to fill bubbles completely and darkly
- Students instructed to stay within written response boxes
Following this list prevents the vast majority of scan failures.
Still Stuck?
If you’ve tried the fixes above and scans are still failing, email support@paperscorer.com with:
- The Reference Hash from the completion email (subject “We have finished scanning your document”) if you used email scanning, or the date and time of the upload from your upload history
- A copy of the original scan file
- A description of what you’ve already tried
Our support team can usually diagnose the issue and get you back on track quickly.