Something you yourself could have tried in the mean time:
[ul]
[li]Read the compile log to determine what shader the warning is issued for (vertex shader, fragment shader or both) [/li][li]Read the compile log to determine the exact line number it occours at [/li][li]If you don’t know alredy, find out what a precision qualifier is [/li][li]Go to that specific line, try adding a precison qualifier and look what happens[/li][li]Alternatively: Not care about having that strange warning on an ATI GLSL compiler as long as it works [/li][/ul]