The AutoCAD Dimension Style that your AEC Dimension Style uses has to be set to be annotative. If your current files were created in a previous release, or in a template started in a previous release, it is likely that the AutoCAD Dimension Style(s) you are using are not set to be annotative. Edit the AutoCAD Dimension Style and, on the Fit tab, check the Annotative toggle in the lower right.
I have not played with this much myself, but you may also need to adjust other settings, such as the text height on the Text tab, if it is not already set to the height at which you want the dimension text to plot.
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David Koch
Autodesk Discussion Group Facilitator
Using ADT 2004 at work; access to 2005, 2006, 2007 & 2008 at home