I've been trying to upload this picture, but I get this error everytime.

Is there any way to fix this?

Probably means the server is fed up with ponies.

Jatix said:
I've been trying to upload this picture, but I get this error everytime.

Is there any way to fix this?

I opened it in gimp and the color profile appears to be normal, so not sure what's happening.

However, the image is not huge, so you could consider smoothing the chroma channel (to eliminate JPG noise) and exporting it as a PNG instead, and try to upload that.
Here's my attempt at the first two steps. I notice that the PNG is actually smaller than the JPG (500k vs 1mb), so yeah.. I'm expecting that there's something weird with that JPG, maybe it has a color profile attached in a non-standard way

Oh, I just looked at it with ImageMagick 'identify', and it is identified as a CMYK image. That's probably the problem. (I didn't even know that JPG supported CMYK!)

EDIT: yeah, identify -verbose shows that it has a pile of stuff attached, most notably a 556k ICC profile.

Overall I think E621 is behaving appropriately. It could try to convert the image to RGB, but that would involve re-encoding it, which isn't really a good idea for JPEG.