Thank you for your post.
Our team hasn't been faced with this issue in the current version.
I kindly ask you to answer for the several questions:
Do you get the same error when opening your project that you have mentioned earlier (Unspecified error (Exception from HRESULT: 0x80004005 (E_FAIL))? If not, which error do you get?
In which versions of TWS did you create your projects that cannot be open in 0.26 version?
Does this apply to all your projects created in the previous versions of TWS?
We will be very grateful if you sent us your 'Activity Log' file. You can do this in Main Menu -> Help -> Report a Bug. Please ensure that the 'Attach Log File' check-box is enabled, and please describe your issue in a few words.
This will help our team understand the reason behind this case.
At the same time, we don't recommend you to use 'copy/paste' option or make other manual changes of the project files. Otherwise, TWS may not work with this project incorrect.