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When I am using the Inverse Dynamics Tool, after editing the external loads, a window shows that 'Tool execution failed', and I checked the Messages window, the error is demonstrated:

'failed to construct ExternalLoads from file I:\OpenSim Model\GR_walking test I\walking data\54321.xml. Please make sure the file exists and that it contains an ExternalLoads object or create a fresh one.
InverseDynamicsTool Failed: ExternalForce:: no force or torque identified.'

I'm pretty sure that I have selected the motions files and saved the XML file after I edited it.

And I tried to edit the file just after saving it, but the error comes again. So the file might have an incorrect format. What kind of faults could cause this problem?

This indicates that the external loads file setup file (.xml) cannot find an external loads data file (.mot). In the .xml file, use an absolute path to point to the location.

Hi：
I am a novice learning Opensim, I would like to consult some questions, when the problems diaplaied above, how to set absolute path specificly，can you give an example？

An example of this solution would be to open the external loads setup file (e.g., "subject01_walk1_grf.xml") in a text editor, find the "external_loads_model_kinematics_file" tag, and replace the relative path or file name (e.g., "subject01_walk1_ik.mot") with the absolute path (e.g., "C:\OpenSim\Models\Gait2392_Simbody\subject01_walk1_ik.mot").

I do the same operation as you said， but the The software still prompts ：
Could not load C:\Uers\Adiministrator\Desktop\GIL\2.4GIL01\GIL01\XSlow2\INVDYN\GIL01_xslow2_Setup_invdyn_ik.xml
Details: object: ERR-Could not find label ground_force_vxin file ../IK/GIL_xslow2_ik.mot. Aborting.

I use Opensim2.4 version to analyze the data about May Liu's walking study and the data she shared: https://simtk.org/frs/?group_id=317， when I use the ID tool, the Message of the software displaied that can not find the grf file, so the analysis have to stopped , so I put forward the question of the grf file , and I have found the reaction force data in IK.mot file before, but what the software prompted me makes me confused, is it because of the version ？ then if I use the 1.5.5 version, can I solve the problem？At the same time ，thank you for your response in time, very grateful for your help and support, thanks again.

It seems that in the .xml, you somewhere specify the external forces. But instead of specifying the external forces .mot file you specify the kinematics .mot where the ground force label does not exist. Have a look at the model examples in the installation folder. There you can see how external forces are specified in the id tool and the .xml file.

http://simtk-confluence.stanford.edu:80 ... d+XML+Tags