Interesting. so something to do with permission then.I'm not sure if it makes a difference, but the error only occurs when the Thor Patcher is located in the directory of the RO Client. If it's located anywhere else in the file system, there is no error at all.
EDIT: I tried to test 2.6.4.13b but I am not able to pack the configuration with ConfigGenerator.exe. It says that it fails. Packing works with 2.6.4.13 but not 2.6.4.13b.
Packing works here, maybe you need move patcher out ro client first or run packer in administrator.