The A-11 came in 2 flavors -- CE 1.0 and CE 2.0 (well, an upgrade ROM). Mobipocket Reader works for CE 2.0 and above. What CE 1.0 device do you have? I have a A-11 in CE 2.0, but I haven't tried using it recently. To be honest, I don't find it much use anymore except that my youngest likes to play with it.
There are several that used to run on my old Mobilepro 400 that I think will run on CE1.0 fine. I guess it depends on your device and cpu. But the names that I do remember were ereader, peekabook, and haalireader. I know that the cab files when you extract them have single .exe files you can copy to your device.
But someone already said that the best method was to just open the file with an existing program, and I agree with that 100%. Calibre is an ebook convertor that will convert nearly any format to any other...and is free. Almost all of my ebooks are in simple .txt format these days and I can use them that way with every device...anywhere.
I don't need all the bells and whistles like with Mobipocket...I only want to read. Now that I'm using my Jetbook Mini...I can do that.