You can use 1.26 but must launch it using a batch file to disable KFX (works up to 1.34). See the first message in the
Dealing with Kindle for PC/Mac 1.19 and KFX in calibre thread and download the batch file mentioned in Method 2a.
And again, update to 10.0.3. See the
New version of DRM removal tools ("DeDRM") for more information.