Hi,
The Blocks can be caused by a lot of different reasons, coding mainly and occassionly hardware. I would look at the following.
1. Dangling objects.
2. Incomplete transactions.
3. Transaction stalled waiting on a triggered call to another locked file.
4. Hardware malfunction. Does one workstation start the problem.
5. Operator doing something weird.

Hope this helps. These can take time to resolve, especially if you didn't write the code or stored proceedures.