This message warns you that the main PDB file to which the executable you are trying to load to AQTime refers does not exist. For instance, this happens when loading Windows system libraries, for which there is no debug info supplied. If you press OK, instead of debug information, AQTime will load information about the functions that are declared in metadata (for managed applications) or in the export section of the chosen executable. This will allow you to profile this file in AQTime, though only partially.