When installing a GTK+ application, configure reports that it can't find GTK. [GTK 2.x]

There are several common reasons for this:

If none of the above help, then have a look in config.log, which is generated by ./configure as it runs. At the bottom will be the last action it took before failing. If it is a section of source code, copy the source code to a file and compile it with the line just above it in config.log. If the compilation is successful, try executing it.