I have the same problem.
If you select all your accounts but a subset of your securities will the report run?
If you hold down the Shift key while selecting Help > About Quicken, how many securities does it say you have? The published maximum is 2,000 but apparently this is a soft limit.
https://www.quicken.com/support/size-or-capacity-limitations-quicken-data-file
Thanks @Jim_Harman . I was surprised to see the Asset Allocation report run after restarting Quicken to check the points you raised. It failed earlier today and has failed repeatedly in the past with the error "Quicken cannot process the selected date range. Please try a shorter date range". I'm not aware of any entries or other changes I made that would cause the report to function - other than restarting Quicken (Windows Premier R48).
I do have a large Quicken file but it doesn't come close to any of the published limits.
Size of QDF file: 329594K Accounts: 47 Categories: 423 Memorized Payees: 52 Securities/Max ref: 318/318 Transactions: 74874
Available Memory: 53415 MB Total Memory: 65373 MB
I'll repost here if and when the issue recurs.