Picasa 3.9 (according to some forums, any version >3.6) throws an annoying error (code #2000009) on saving some JPEG files, if one wishes to save the edits done in Picasa on that file. The error message wrongly says disk error, when the actual cause is XMP data that was saved with that JPEG file using some other editor (GIMP, for example) before opening it in Picasa. Obviously, the issue is present on both Windows and Linux (i.e. Picasa on Wine).
Google product forums suggest the issue is there for a while. The issue is probably with the way Picasa parses the XMP data and tries to write something in the metadata that states the image was last edited with it. Many image editing software do the same, but with Picasa there seems to be a fault that prevents one of the very basic functionalities of an image editing application – i.e. saving the image.
This error can be avoided if in the first application we remove the XMP data from the JPEG file, then open it with Picasa. In this way, there is no XMP parsing issues and Picasa saves the file correctly. In GIMP, this can be done by simply unchecking the “Save XMP data” box in the “Advanced Options”, when an image is exported as JPEG (you can still retain the EXIF* info by keeping that option checked):
So if your workflow involves editing with GIMP or some other heavy duty image editor before (which is obvious) experimenting with the “effects” in Picasa, and you are running Picasa above 3.6, then uncheck this box in GIMP to avoid this error later when you save it in Picasa.