I am using the same AutoCAD software in the same PC. I opened a new acadlt.dwt and were able to draw lines with "DIM" command working properly (with text shown up). Then I saved it as a dwg file. No problems with the "DIM" command when I reopened it. However, I have another existing dwg file (not created by me), but I couldn't use the "DIM" command with text shown up.
I couldn't see any setting differences between the two files so far. Could somebody have any idea on where the problem is?