If you suspect a locking issue with your SQL Server database, this is how you can check with SQL Server 2005.

1. Launch Microsoft SQL Server Management Studio
2. In the left panel, click Management > Activity Monitor.
3. At the top, click the 'Filter...' button.
4. In the Resources section, enter the name of your database.
5. Click OK to apply.
6. Scroll to the far right and check for 'Blocking' and 'Blocked By'.

Thanks to McG for the tip.