I have had this same problem on a few of my reports.  It seems to make a difference with how I use the field.  I think if I tab through the field, the error happens, but if I click through I can avoid it.

Very frustrating.

This has been happening to me for the last 2 weeks. I too am using reports that I have used for years. The only way I have discovered to make it go away (temporarily) is to copy the user defaults of another employee to my user. Very frustrating as I have many settings that I have to then go and reset to my defaults.

I made a copy of an old user's reports as well, and it worked for a bit, but now that one seems to be corrupted as well. So, yes, I agree that the solution is only temporary, and such a waste of time!  

No word back from any Sage employees yet??

I spoke with Sage support when this first happened. That's how we discovered the temporary work around. No word as yet as to a permanent fix. 

Looks like my error is slightly different.  Here is a screen shot I just got from the stock 11-1-10-21 report. 

If I enter something in the first "period" field and then tab to the second "period" field, this error comes up.  If I instead use the mouse to click into the second field, there is no error.

So this is happening again (!) to a bunch of my reports that i've used for years!  Any fix for this yet???

Still getting this error... 

I've had to re-set two other users now.  Total waste of time!

Here's a knowledge article on the issue: https://support.na.sage.com/selfservice/viewdocument.do?externalID=85416