Hello Viliam

As mentioned in the other topic, sometimes this error can appear when something went wrong while saving the files.

When this happens, check your project folder. You might find some files named xxx.xml_tmp

If you do, simply replace the old files with the _tmp version and the project should start working again.

If you do not find any such file, try and delete the file named fonts.xml and try opening the project again

Keep me posted on this here

Thank you

Stefano