The knowledge base contains instructions for fixing the problem:
mbs2.microsoft.com/.../kbdisplay.aspx
CAUSE
This problem may occur if an invalid record exists in the SY00500 table.
RESOLUTION
To resolve this problem, follow these steps; 1. Have all users exit Microsoft Dynamics GP.
2. Use the appropriate step: • If you are using Microsoft SQL Server 2005, start SQL Server Management Studio. To do this, click Start, point to Programs, point to Microsoft SQL Server 2005, and then click SQL Server Management Studio.
• If you are using SQL Server 2000, start SQL Query Analyzer. To do this, click Start, point to Programs, point to Microsoft SQL Server, and then click Query Analyzer.
• If you are using SQL Server Desktop Engine (also known as MSDE 2000), start Support Administrator Console. To do this, click Start, point to Programs, point to Microsoft Administrator Console, and then click Support Administrator Console.
3. Run the following statement against the company database.
Delete SY00500 where BACHNUMB = User_ID_Of_The_User_Who_Receives_The_Error_Message
If the problem persists, see Microsoft Knowledge Base article 852623. For more information about how to resolve this problem, click the following article number to view the article in the Microsoft Knowledge Base:
852623 Error message when you try to open the Sales Transaction Entry window in Sales Order Processing in Microsoft Dynamics GP: "Your previous transaction-level posting session has not finished processing"