If you are not able to view Task Details page Dont access OIM using localhost.
Go to Command prompt --> Type host name
For example if you get 'CompUser' access the OIM URL like this
Now your Task Details page should work absolutely fine.
The second part is not my concern, what i am assuming is it can be the browser issue or some host issue.
But the issue is it is throwing the exception for rejecting the request at first level if we are not checking the task details. But at second level we are able to reject the request without even checking the details.
In my workflow, I have two Human tasks for two different level of approval. My thought is that using two Human task is creating this inconsistent behavior.
Check the instance ID in enterprise manager and look at the Audit Details .., what is the error message there ?
Just in case you are using the Oracle documentation on creating a custom taskflow if you have put the toolbar in the top of the stretchpanel layout this gave me this exact issue until I removed it from the top and just left it within its original context within the Task Information tab.