Are the message actually showing four digit years?

Are either the long date or short date settings for your dates in Simply Accounting set at two-digit?

If so, change both of them to four digits.

Thank you for your help! That was exactly the issue: problem solved

Richard S. Ridings said:

Are the message actually showing four digit years?

Are either the long date or short date settings for your dates in Simply Accounting set at two-digit?

Hi Thomas de Homem-Christo, if the above suggested answer helped, please do mark it as verified for the benefit of others in this forum. Thank you!

Richard, I am having the same problem with Simply 2010  I have closed 2020, (and set my session date at 31/01/21) and I am getting an error message that says "Invalid date. The start date must be between 01/01/15 and 31/01/21."   My start date on the Income Statement I am looking at is set at 01/01/21 to 31/01/21.  I've used this program for years and have never seen this problem before.  I appreciate your help. 

Well, blow me down!  I did that thing, changing the date format to "long date" and now it works just fine!  Doesn't make any sense to me, but it worked!  Thank you, Richard!