I use the same version of AutoCAD and I had x_t files without any issues - AutoCAD may take a longer time to get it open, it depends on the file size.
Is your file damaged?
And other thought is that the version of x_t - I could be wrong.
Is your x_t file the latest version? Can AutoCAD mech 2016 open the latest version of x_t?
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From HELP:
"Import" command.
In Files of type, select the file format to import. In File Name, select the file name to import. The file is imported into the drawing.
The following formats are available for import for AutoCAD.
...
JT (*.ij)
Parasolid (*.x_b)
Parasolid (*.x_t)
Pro/ENGINEER (*.prt*; *.asm*)
Pro/ENGINEER Granite (*.g)
...
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A circle is the locus of a cursor, starting and ending at the same point on a plane in model space or in layout such that its distance from a given coordinates (X,Y) is always constant.
X² + Y² = C²