Quick answer
The most common upload error on the web is still some version of file too large. Sometimes it appears as maximum file size exceeded, upload failed, invalid file size, or this document is larger than the allowed limit. Different wording, same problem: the website wants a smaller file.
For images, the fix is usually to reduce file size with the right format. JPG works well for photos, while PNG is often better for screenshots or graphics. If the portal only cares about size, it helps to aim for the limit directly instead of guessing through repeated retries.
What usually works best
For PDFs, the situation is more complicated because the file can contain scans, photos, text, or multiple pages. When a site rejects a PDF, it usually means you need a smaller final document, not just a different filename. That is where exact PDF targeting becomes useful.
A second layer of errors happens when the file size is technically small enough but the upload still fails. In those cases, the issue is often image dimensions, unsupported format, or a poor-quality scan. That is why ExactSizer now includes resize controls for images and profile controls for PDFs.
If it still fails
A practical way to solve these errors is to fix one thing at a time. First reduce the file to the stated limit. If the website still rejects it, change the dimensions, switch to JPG for photos, or use a stronger PDF setting. That order fixes most upload failures people run into on forms and admin portals.
This is especially helpful for people applying for jobs, visas, admissions, or public services because those sites often use older upload systems with strict rules and unhelpful error messages. A tool built around exact limits saves time every time the website refuses to explain what went wrong.