Uploading avatar fails

[Alphakilo23]

I tried to change my avatar by uploading an animated gif (128x85 pixels, 89,25 KB) to my webspace and using Option 1 in the Edit Avatar menu. It fails with an vBulletin message:

"Upload failed due to failure writing temporary file."

I tried clearing my cache, using different browsers, nothing helps.
If I upload from my own computer the gif appears as a still image of frame 1.

 

[MentaL]

Try now.

 

[Alphakilo23]

Try now.

Uploading works, but the animation doesn't. But I strongly suspect my mobile provider to interfere.

Thanks.
EDIT: Turns out I had to resize it down to 100x66, despite being an subscriber :<