Customers who have defined there own utility classes and then IMPORT them into a custom script may find that they see the error "unable to resolve class" when using their custom script file within the Jira Web Interface.
First, make sure that your package names are correct. Remember that Scriptrunner makes a default script roots directory called "scripts" under the Jira Home directory. If you use this default directory, your package names will start from the folders under the script roots (excluding the "scripts" directory itself). The Jira server can see into the scripts folder and any directories within.
If your package names are correct and you still see the "unable to resolve class" error then you are likely on a version of script runner older than 5.4.42 which is impacted by the following bug:
The solution to this would be to upgrade scriptrunnerto a version after 5.4.42