"Unknown command "DDEDIT""
Nathan:
I assume that the items on which you are double-clicking are Text, MText or Attribute Definition objects. Are you using Any chance that you have brought forward a custom ACAD.pgp file, either by using the Autodesk migration tool or by manually copying your PGP file from a previous release?
The DDEDIT command was discontinued with the 2015 release. The 2015 ACAD.pgp file includes a line to define DDEDIT as TEXTEDIT, which is the "new" command (added in the 2010 release) for editing Text, MText or Attribute Definition objects. The ACA.cuix file in 2015 (and, perhaps, many other customizations created by Autodesk and others) still references the DDEDIT command as the double-click action. While adding DDEDIT to the PGP file is a good idea to keep third-party customizations running, I would argue that when Autodesk decided to discontinue the DDEDIT command, they should also have replaced any reference to it in the out-of-the-box files (other than ACAD.pgp) with TEXTEDIT. You can either edit your CUIX file and replace the references to DDEDIT in the double-click action section with TEXTEDIT or add DDEDIT to your ACAD.pgp file, defining it as TEXTEDIT. (Or do both, in case you have other places where DDEDIT is still referenced as a command.)
The out-of-the-box ACA.cuix does not have a double-click action assigned to dimensions. What action would you like taken when you double-click a dimension? You could add the DIMENSION object to the Double Click Actions node, and then assign a command to it. When no action is assigned, it should default to opening the Properties palette.
PS: I suspected that you did not migrate settings, but threw that in there for others who may read this later. I do not migrate settings, but I have been known to copy an old PGP file forward. I usually try to cut and paste my customizations onto a copy of the out-of-the-box file for the new version, just to avoid issues like this.
I do not have an installation of ACA 2013 to check, but I could not find a double click action assigned to dimensions in 2010, 2014 or 2015.
That said, it sounds like you had one assigned in 2013 (whether out-of-the-box or customized). I did find that the ACAD.cuix file had the TEXTEDIT command assigned as a double click action in 2014 and 2015, so 2013 may also have had that and you may have transferred it to the ACA.cuix (via the Transfer tab of the Customize User Interface dialog). Using TEXTEDIT on an AutoCAD Dimension object does allow you to do on-screen edits, which are treated as dimension text overrides.
FWIW, I usually use the Dim prefix and Dim Suffix properties (Primary Units subcategory) when I want to keep the true dimension and just want to add text before or after. But that is just me. (Dim prefix and Dim suffix values are copied by Match Properties; Text overrides are not, and have to be done for each dimension. Both have their uses.)
