I got problem when buying new item

[l3minh]

When I click "Buy Now" to buy new item, it generates this error after waiting for a while:

Lock wait timeout exceeded; try restarting transaction
File: /usr/local/psa/home/vhosts/mydomain.com/httpdocs/download/forum/Sources/shop/Shop.php
Line: 212

Pls show me how to fix this error?

[Daniel15]

I have no idea what that means, I've never seen it before.

I'll try and look at it when I have more free time.