I am not sure about AX4, but in AX2009 ReleaseUpdateDB is in the sys layer. I had a similar error during my AX2009 to AX2012 upgrade because there were modifications to the releaseUpdateDB classes leftover from the AX3 to AX2009 upgrade. I removed the mods and reimported the XPO.
Yeah you are correct, ReleaseUpdateDB does exist in version 4 in the Sys layer. As instructed, I import the AX4 upgrade XPO from the 2012 R2 CD and then compile the AOT afterwards.
I have debugged the code and I cannot see the exact error - this is causing me major issues - can anyone else shed some light on this towards a solution?
Update: If I manually assign the enum value inside the parmScriptStage method - I can access the form options - the values are not being passed correctly into the parmScriptStage method, I appear to be able to work around this, however it must be Microsoft issue, I am amazed there are not more AX4 users that have experienced this in their upgrade attempt.
You don't mention if you are slipstreaming an update along with AX2012 R2. There is an upgradeax4.xpo file dated 10/31/2013 in the CU7 DatabaseUpgrade directory, so perhaps the problem was fixed with an update.