is this a dreamweaver question?
No, it is not. I haven't built the website myself, I have a provider for this (who is puzzled with this as much as I am). The funny thing I just discovered is that the problem occurs when I have resized the image for use on my website. When I upload the original (not-resized) image, this happens successfully. I usually resize my images in Photoshop using Automate > Fit Image > Width 1800 px, Height 900px. This has worked fine for me for years but apparently something in Photoshop 2015 has changed.
is your question related to an adobe product?
if you're asking whether an adobe program (eg, ps) could produce a file format not allowed on your server, the answer is yes. but whether it is producing such a file type or not depends on your servers allowed mime types.