I'm assuming you're using an SQL database here... a quick Google has found this as the explanation for that error code:
This error occurs when Microsoft® SQL Server™ encounters a deadlock. A deadlock occurs when two (or more) processes attempt to access a resource that the other process holds a lock on. Because each process has a request for another resource, neither process can be completed. When a deadlock is detected, SQL Server rolls back the command that has the least processing time and returns error message 1205 to the client application. This error is not fatal and may not cause the batch to be terminated.
technet.microsoft.com/en-us/library/aa258770%28v=sql.80%29.aspx
Essentially the table you're referencing in your report is already locked by another report/process and so it cannot send the query. You may be able to find a solution on that link.
Thanks,
Andrew