You are either missing a jar file (org.apache.commons.io) or you have a duplicate version in the lib folder of your mendix application's directory.
If you have a duplicate version of this jar file remove the oldest version and clean the deployment directory from studio pro and restart your app. This is probably the cause.
I remove org.apache.commons.io-2.3.0.jar
and commons-io.commons-io-2.11.0.jar
and it worked for me.
This was a gnarly one for me. It took me a whole day to figure out, part of which I spent researching the commons.io github repository to determine which version of commons-io introduced the Builder() method.
This is what I did to resolve this error: I deleted several duplicate jar files as most answers suggested but it didn't fix the problem. Thankfully, the userlib folder now has what I call "comment" files that indicate what modules are dependent on a particular jar file. So I looked for all the jar files that are dependencies of XLSReport and ExcelImporter and deleted older versions of the jar files. The files I deleted were:
Once I deleted these jar files, the error went away. I hope this helps someone else avoid a whole day of jar file hell.