Make sure that the CPU you are trying to download to is in RUN-P or PROG mode (not RUN).
Check the specific error you are getting in the diagnostics window. There should be additional information beyond just the error you saw on the screen. Do a consistency check (File/Run Consistency Check). Often this check will reveal the issue.
Lastly, for the timer issue, try deleting the timer and adding it back by dragging in a "fresh" instance of the timer from the block library.