Few days ago while working with importing customizations and re-freshing AOT in Dynamics AX 2009, we stuck with the following error "Illegal data conversion from original field [field names]Unable to convert data types to anything but character field type (0 to 4)." Found a great blog on that topic. Hope, will solve, if you  stuck with similar problem. Click on link read blog http://daxline.blogspot.com/2011/07/how-to-fix-illegal-data-conversion-from.html.