To proceed with a TAC case you always have to provide tech support file which can be generated via GUI, Device - > Support -> Generate Tech Support File.
If this works, there is no issue, but this is not always the case :) 

If it gets stuck, you can use cli command
>request tech-support dump

But, if GUI option gets stuck, it is highly possible this will not help either. The solution is to interrupt the "show or debug" command which prevent process to generate the tech support file.
Use this CLI command:
>scp export tech-support to user@host:/path/

This will allow you to interrupt (using CTRL+C) the stuck command and carry on in generation of the file.