I use both. When I post and want to include photos, I have to click the manage attachments icon below the text box. I have to upload them to "my attachments" and click done, then when I click "submit post", the photos trail in from my attachments. I have never tried from my Windows based laptop, so I'm not sure the difference from PC or IPAD/IPHONE.
That's how I used to do it as well, now I get incorrect file message - they are jpeg so shouldn't be a proble,. Also can't drag and drop pictures in library.
I find it easiest to use Photobucket... It's free and the pics show up large sized. I upload all my pics to photobucket and it's a really convenient tool. I can even text the pics right to the site Right from my phone.
I've never uploaded from the iPad mini, let's see if it'll work... Nope, same error you got. Image is likely too large, I'll try something smaller. Ok so I know crap when it comes to Apple products, but I can't find anyplace it even shows any details about the image specs, or a way to resize it when selected to view or edit. Sorry I'm no help with this.