First of all make sure you are using the latest WinUAE. Also make sure the logging options of WinUAE are enabled so whenever it crashes, and you suspect it's due to WinUAE bug, send the logs together with the description to the author of WinUAE.
With regards to the hardfile, it might happen it's not valid, especially if you use FFS or similar filesystem. Try to boot without startup-sequence with the hardfile mounted and let it validate. Simply wait till the HDD led activity is gone.
Another solution would be to mount the hardfile to some already pre-configured emulation package like AIAB or AmiKit and access it from there. Just to check whether it works.
I personally always backup the hardfiles. It's so simple as it's only one file.
