This error occurs when a TDL file(%s) is included more than once as a part of another TDL file.
Remove the repeated inclusions of the file.
Example
The file myreports.tdl is included twice in the file Main.tdl as given below:
[Include: myreports.tdl]
[Include: myreports.tdl]
When the file Main.tdl is compiled, the message error T0003: file 'myreports.tdl' is loaded already. appears.