The BitLocker in Windows 10 keeps giving me an error with a message

You could check the Local Group Policy if the following is enabled:
Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption\Operating System Drives
Setting: Enable use of BitLocker authentication requiring preboot keyboard has to be enabled In Group Policy
Enable it, then open up a command prompt and run a gpupdate /force

Is this while trying to encrypt with BitLocker, or the drive is already encrypted and you get this startup error?

If you are trying to encrypt, I would suggest that you make sure BIOS is up to date. Win 10 BitLocker works best with the latest and greatest TPM version and support in BIOS.

Regards

Win 10 BitLocker works best with the latest and greatest TPM version

Though that's not always the case. https://www.experts-exchange.com/questions/29123695/The-BitLocker-in-Windows-10-keeps-giving-me-an-error-with-a-message.html?utm_source=experts-exchange&utm_medium=email&utm_campaign=followed_topics
 - (Second to last post) Sometimes downgrading TPM can resolve the issue

But I wouldn't worry about TPM until after you tried the suggestions made by ITguy565.

@kenfcamp - good to know, however your link seems to point back to this question so we don't have a reference to the downgrade TPM post.

My experience with Dell Optiplex has been to ensure BIOS is up to date, but it seems your mileage may vary. Would still like to know from the author if this error was during startup of an already encrypted drive, or during the attempt to encrypt the drive.

Regards

Got it, thanks for the info Ken.  Seems that indeed TPM 2.0 could be the culprit in this case.

Thanks for your help.