The problem is that you were trying to open an image in GIF format,
which uses an indexed mode, meaning all colours used in the image are
defined in an index of 255 colours, and any colours not defined in the
index cannot be used in the image. This means that images can't be
blended, for example using iWarp.
A greyed out item means that although you have the plugin, you can't use
it on that image or the current selection, for whatever reason. Try
opening a JPEG file and you will see the distorts menu now has a lot
more options available, including iwarp.
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