The key portion of the error message above is "WIMCaptureImage failed - GetLastError returned 32 (The process cannot access the file because it is being used by another process.)".
The error 32 is being returned by Dism.exe which is part of the WAIK. Boot Disk Creator calls Dism.exe to create the wim file used as the boot file for PXE and other boot media. The most common cause of this type of error is antivirus or other security software placing a file lock on the wim file which prevents Dism.exe from unmounting the file.
To workaround this issue, temporarily exclude your antivirus or other security software from scanning the "C:\Users\<currentlyloggedinuser>\AppData\Local\Temp\" folder or temporarily exclude files called boot.wim from being scanned.
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