Well, I'm not sure how to help you with that problem, as I just tested it here using 4 different browsers... Safari, FireFox, MS Internet Explorer and Google Chrome. They all worked fine uploading multiple pics of different types.
I notice you're using FireFox 45.0 running on Windows 10. Have you recently upgraded either of these? The site's Advanced file up-loader software uses Java/Flash to handle the uploads. Are these add-ons current and active (not blocked) on your computer?
Here's a bit of a primer on how uploads work on our site..
First, there are two kinds of upload capabilities available, Advanced (select multiple files simultaneously, use drag and drop with mouse etc..) and Basic (select files one at a time). When you select Manage Attachments to upload files and attach them to any post, you start with the default Advanced screen. Using your personal Edit Options (click here) page, you can set which back and forth as to which method is your personal default.
Attachment 71036
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You can also select and switch to the Basic method of uploading from the Advanced screen, even though your default may be set as Advanced.
This is the Advanced screen and you can switch to the Basic method while viewing it.
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This is what the Basic screen looks like after you've selected that method while viewing the Advanced screen.
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Have you tried uploading to our site by selecting and using the Basic screen uploading method?
Finally, I need a LOT more information to trouble shoot your issue much further. When you say ... When I select upload, each photo slowly displays an error. Nothing is uploaded., do you actually mean it's a red exclamation mark ! as in this screen pic?
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If not, please provide a step by step sequence of what you're doing and if you wish, email that to me (with pics of the problem) to badger@milsurps.com.
Hope some of this helps you ..
Regards,
Doug