See the below blog for a possible fix:
blog.encorebusiness.com/dynamics-gp-error-messages
Q2: When I try to post a batch in the General Ledger module, I receive the following message:
Batches cannot be posted while the Year-End Close is in progress.
The year-end closing routine is not being run in General Ledger. What should I do?
A2: To resolve this issue, have all users close all transaction entry windows. Then, delete the SY00800 file if you are running a Microsoft SQL Server database. To do this, run the following statement on the DYNAMICS database.
delete SY00800 where BACHNUMB = ‘GL_Close’
For more information, click the following article number to view the article in the Microsoft Knowledge Base: 856550: (support.microsoft.com/.../856550 )
Error message when you try to post a transaction in General Ledger in Microsoft Dynamics GP after the year is closed: “Year End Close is still in process and batches cannot be posted”