GIMP Version: 2.8.14
Operating System: Linux
OS Version: Kubuntu 14.04-5
GIMP Experience: Experienced User

List any ERROR messages you received:
See picture

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My wife gets this error when she opens one or several files. Gimp is in this situation totally non-working.

Can anybody help?

See Edit>Preferences>Environment>Tile cache size. When Gimp needs memory to keep images, it either grabs more RAM (increasing the tile cache size) or writes them to disk in a temporary file, which is normally in her Gimp profile.

Normally you set the tile cache size above to something that lets Gimp grab a lot of RAM without choking the rest of the system (typically, you would use RAM size minus one GB on Windows, and RAM size-512M on a Kubuntu). When Gimp needs more that this, it writes to temporary file on the disk...

So the message above is telling you that 1) Gimp has grabbed all the RAM it is allowed to use and is writing to the disk, and 2) the disk is full. So the question is where is her Gimp profile, and how full that disk is.