Following is a copy of a message posted on the mailing list some time ago:
MESSAGE:Re: Web Page Uploading Problem-AGAIN! AUTHOR:Melissa DATE:Tuesday, 24 August 1999, at 4:34 a.m.
Response To:Re: Web Page Uploading Problem-AGAIN! Author:Laurie Kenville Date:Monday, 23 August 1999, at 7:45 p.m.
I was testing this and I don't think that February is the problem. The same message will appear if the month you enter in the Go To field matches the number of months in the Deviation field.
For example, in your original test, you entered February in the Go To field and 2 months in the deviation field. If you enter April and put 4 in the deviation month field, you'll get the same error -- or December and 12 in the deviation month field.
So as long as the number of months in the Deviation doesn't match the numeric number of the month in the Go To field, it appears that you won't get the error.