This will be fixed in the next version. The Linux 2.6 (32-bit) icon had the 64-bit image for some reason. This only affected that particular guest OS icon.
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On 32 bit system showing 64bit icon
version phpvbox is 4.3-1
http://i33.fastpic.ru/big/2014/0408/e1/3df6cbd7f66a88de9544b608cdbdb5e1.png
This will be fixed in the next version. The Linux 2.6 (32-bit) icon had the 64-bit image for some reason. This only affected that particular guest OS icon.