Max plug in for iclone 5 only works with 32bit, while max plugin for iclone4 works with both 32bit and 64bit.
Also your virus scanner might remove the plugin files and will give an error when launching 3Ds Max. As it did with mine. Just download the plugin again, add it back in and excluded it from future scanning on your anti virus software if that's the problem.
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My latest release for CC
For all my other iClone contents, click here.