Where did you try to upload this? your own wiki or on commons (using the upload wizard)?

Adding testme keyword to try and get more info

Possibly related to bug 39303

Valerie.m.juarez wrote:

Using Firefox 12.0 on http://test2.wikipedia.org/wiki/Special:UploadWizard I was able to upload a file with an underscore in the file name. The published file's name replaces the underscore with a space. I was not able to upload a file using IE, but I don't think it has to do with this issue.

Below are the steps I took:
I created an image file in paint and named it "waving_person.png".
At http://test2.wikipedia.org/wiki/Special:UploadWizard
-I passed through the tutorial
-Selected 'Select a media file to donate'
-Navigated to the image "waving_person.png"
-Selected the image in the window and pressed 'Open'
-The image successfully uploaded.
-I selected 'Continue'
-Selected the 'This file is my own work' copyright and pressed 'Next'
-I added a description and published the file
-The filename changed to "Waving person.png"

I attempted to upload another file with an underscore in the file name on IE 9.0, but the upload got stuck at the "Getting file information and previews" part of the upload. I tried uploading a file without an underscore in the file name, but it still got stuck, so I do not think the problem is related to this issue. I will investigate this problem.

Valerie: Interesting findings with UploadWizard, thanks.

This report is about the "traditional" upload interface which will be replaced by UploadWizard in the long run, so it's interesting to see that the problem likely won't exist anymore once we've completely switched to UploadWizard.

For the IE issues that you face with UploadWizard you could file a bug report against product "MediaWiki extensions" and component "UploadWizard" once you've tracked them down a bit and after checking if a report already exists.
Could be also interesting to mention whether you use IE's "compatibility mode".

(In reply to comment #5)

Valerie: Interesting findings with UploadWizard, thanks.

This report is about the "traditional" upload interface which will be replaced
by UploadWizard in the long run, so it's interesting to see that the problem
likely won't exist anymore once we've completely switched to UploadWizard.

I doubt its about the traditional upload form. “Unknown error: "unknown-warning"” Is an API error, which the traditional upload form does not use.

I note that the filename in the original report has both an underscore and a space, which might be important in reproducing the error.

At first glance, I don't know where "unknown-warning" might be coming from. I only see that in the UploadWizard code, but I don't think the UploadWizard extension affects API uploads at all. Or is this UploadWizard-related and not API-related?

marklarcher: Could you please answer the open questions in this report, and clarify how exactly you tried to upload?

Unfortunately closing this report as no further information has been provided.

marklarcher: Please feel free to reopen this report if you can provide the information asked for and if this still happens. Thanks!