I don't see any irregularities in the .htaccess at firs sight, so let's rule that out for a second.
The only difference there is the folder and the file permissions. It is possible that if the file/folder permissions are above a certain level, the server might not serve them. I believe it's some kind of protection.
So, you should try to change the permission of the asp_upload folder to the same as the others (I guess it's 775), and do the same for the file permissions in the asp_upload folder (.
As a test case, you can try making another folder in the uploads folder, for example 'test' with permissions 0777 and put a file in there and chmod that as well to 0777, and see if you can reach it via browser. If not, then there is definitely a restriction on permissions, and it should be lowered until the file is reachable.Best,
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