Start with the exact message and a small known-good image. A rejected file type, a request that fails during upload and an image that cannot be processed after upload are different problems.
Compare a small test file
Try a modest JPEG or PNG you are allowed to upload. Give it a simple filename and upload through Media → Add New. Note whether it appears in the library and whether its preview or generated sizes are available.
If this succeeds but a large image fails, check the displayed upload limit and the source dimensions. A highly detailed image can require substantial processing memory even when its compressed file is not enormous.
If every file fails, test another browser session, confirm your account can upload files and check hosting storage. Record the timestamp so the host can find the failed request.
Check the limit and storage
The maximum upload size reflects server configuration as well as WordPress. Ask the host to confirm the allowed request size, PHP upload limits and available disk space. A browser retry does not solve a full disk or a server rejection.
Resize a copy of an oversized source image and keep the original elsewhere. Do not repeatedly upload the same huge file while trying unrelated plugins.
If upload completes but processing fails
Ask the host whether the image-processing libraries and resources support the format and dimensions. WordPress's generated variants depend on server capabilities. Format support on one installation does not establish support on every host.
Check whether an image-optimization plugin intercepts the upload. On staging, repeat the same small-file test with that feature disabled. Follow the conflict process to isolate the component rather than disable everything on production.
If the uploads folder is not writable
Ask the host to verify ownership and permissions for the correct uploads directory. Do not set folders to unrestricted 777 permissions as a general fix. Different host environments use different ownership arrangements, and broad permission changes can introduce another problem.
Preserve the existing permissions before any approved adjustment. A message about a directory can also refer to a wrong configured path, so verify the path before changing access.
Gather a useful support report
Include the exact error, file type, byte size, pixel dimensions, upload method, browser, time and whether a small test succeeds. Share sensitive logs privately and omit credentials.
After a fix, upload a new small file and the resized problem file. Confirm their public URLs, library previews and rendered page appearance. Do not delete a partially uploaded file until you know whether existing content references it.
Sources & verification
Sources checked October 7, 2026. Documented behavior is distinct from hands-on testing.