Rerun task

Yes there is.  I have done exactly this within the last 24 hours on a machine where the entire cache of GPU tasks became 'compute errors'  (apart from two that were sitting there 'ready to report'.  Before going any further, let me point out that the simplest course of action is to do what archae86 advised.  If you're interested, I'll explain what happened in my case.

My problem was because of a current heatwave.  Today's temp was 36C and tomorrow is predicted to be 39C.  The machine was still crunching CPU tasks but the GPU tasks failed because the GPU app was deemed by BOINC to be corrupt, despite the fact that GPU tasks were crunching.  From time to time BOINC seems to perform a checksum test and for some reason the check failed.  I've had this happen before.  The app isn't actually corrupt.  The routine that works out the checksum seems to get it wrong sometimes in high ambient temperature situations.

Be that as it may, the reason isn't important.  The upshot is that there is a host in distress, also with about 50 failed tasks in a ~18 hour backoff that will count down to zero before all the failed tasks will be reported (unless I click 'update' to override the backoff).  A mass failure like this seems to cause these lengthy backoffs.  I don't really know why but I'm forever grateful for it.  It allows me to retrieve the entire cache of work rather than trashing it.

The recovery procedure involves setting NNT (no new tasks) in BOINC Manager, then stopping BOINC and editing the state file (client_state.xml).  This is NOT a normal or routine procedure and should not be attempted unless you have a really good quality plain text editor and a decent understanding of the structure of the state file.  All you are going to do is cause your BOINC client to 'forget' about all the failed tasks by simply deleting them.  Each separate task is bounded by <result> .... </result> tags and you need to delete every single one of them.  On mass failures like this, it's usually pretty simple because the failed results are usually consecutively listed in the state file.  If you identify the start of the very first failed task and the end of the very last failed task, and if there are no 'good' tasks somewhere in the middle of the list, you can delete the whole lot in one simple operation.  It's pretty easy to recognise a failed task.  There is the failure message embedded in each one so they are really obvious.

There are also a lot of <file> .... </file> blocks that are associated with the tasks that have a <status> of zero normally.  An error status of -161 seems to get inserted in these.  I suspect these can probably be ignored as the removal of the <result> blocks probably causes BOINC to remove the associated <file> blocks anyway.  I usually do a global search and replace to change all such -161 values to zero and it's always been successful.  Next time I might just delete the error <result> blocks and leave the -161s and see what happens :-).

After editing and saving the state file, I restart BOINC.  There are no complaints (if I'm careful to avoid mistakes) and the tasks tab now shows just the ones that weren't errors.  With NNT still set, I 'update' the project.  This causes the client to tell the server exactly what it has on board.  The server immediately notices all the missing tasks and graciously sends you fresh copies in batches of 12 per 'update'.  It will tell you (very politely - how amazing :-). ) that it's "resending lost tasks".  Very quickly, you can have the entire cache restored to its former glory.  At that point, remove the NNT and you will be back to normal operations.