There is a serious problem with the new update of the Liquid Xml and i can't figure it out.
We have seen this on some PCs, it looks like a DDE timeout issue which we are working on a resolution. We see the file does actually open, but Windows shows the error as you describe. Is this what you see, or does the file not open either?
Do you have a specific schema, or any schema? E.g. if you open the sample project and open the BookStoreSample.xml and press F7 do you get the issue?
If you want to uninstall, you can do so using the 'Change or remove a program' from Windows Control Panel. You can then download and install the 2016 version:
https://www.liquid-technologies.com/my-downloads
Note: you need to login as the user who purchased the license.