It means that
Either Date of Entry is Incorrect
or
Current Period Selected is incorrect
or
Date while making Company was Incorrect
If Date is Incorrect
Change date by Pressing F2
Current Period Selected is incorrect
Go to Home Page(Gateway of Tally) by Pressing Esc
Change Period by pressing Alt F2
Suppose we want to pass entry on 10 May 2016,period should be 2016-17 i.e.from 1/4/2016 to 31/03/2017
Date while making Company was Incorrect
Company Info--->Alter--->Select Company
Check both dates
Financial Year Beginning from
Books beginning from
Both dates are normally same (Suppose we want to pass entry on 10 May 2016,period should be 2016-17 both Financial Year Beginning from and Books beginning from dates should be 1/4/2016
(Some people wrongly put 31 March in books beginning from)