SciLexer.dll is missing or not found
I am afraid what you say is impossible unless you have not installed it with the official installer that can be downloaded from https://sites.google.com/site/rfodesigner/
I have just double checked by reinstalling to verify whether the "SciLexer.dll" is included and it is affirmative and working as it should.
Maybe your antivirus software is the culprit ?
What should you do? Uninstall RFODESIGNER and reinstall, making sure that your antivirus software gets permission to allow all files.
If you have projects saved then you must make sure that you have a backup of them, just in case.
RFODESIGNER must be on the C: drive and must have admin rights to work properly.
The included RFO2APK which is used to compile your APK on the fly needs the Microsoft Dot Net Framework installed and a link to that can also be found on the website.
Be aware that Version 2 is only compatible with version 2 examples.