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As it turns out, this error is caused by bad data in one of the user Attributes. The good news is that it can be fixed, the bad news is that it may require some perseverance to find it. The following steps and screenshots were done on a Win2k8 controller so some things might look different. The user and computers MMC is currently in 'advanced' mode (View-> Advanced Features)
Open up a known good user that you can copy and on another window or another dc open up the problem user. Go to the Attributes Tab and set the Filter in the bottom right to "Show only attributes that have values" and repeat in the other window. (That is unless you like spending LOTS more time doing this). This will narrow the search down considerably.
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Now do a side by side comparison and look for values that either exist in only one user or that look odd.
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In my case, when I went to Edit the msRADIUSCallbackNumber attribute, I found that it had garbage in it. Just hit the Clear button and OK out.
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After I torched the msRADIUS values on mine, I was able to copy the user without any problems. And due to a shortage of time, I didn't get around to writing a powershell script to dump it out to excel but maybe if I get bored one day...