Had the same issue when upgraded my project from 6.5.1 to 7.8. Had Java compilation errors related to cloud services. Then after App Store, Download AppCloudServices 1.4, replace in my project, I got the errors you describe. What was strange, the referenced microflow existed in my project, but probably in a different path. The solution was just to re-select the microflow Administration.OnFirstLoginAppCloudUser in InvokeOnFirstLoginAppCloudUser and the errors were gone.
I found the answer to this in Mendix's reference guide.
offers a detailed description on how to incorporate AppCloudServices into an existing application.
After setting things up as described in the guide my existing mendix application worked fine with AppCloudServices and