What is the location of this Application's file? This application shows in Finder at path (with target):

Macintosh HD/Applications/Trans_Helper.app/Contents/MacOS/applet


and I have not been able to successfully start it with launchd, using

~/Applications/Trans_Helper.app/Contents/MacOS/applet
//  or
/Users/myusername/Applications/Trans_Helper.app/Contents/MacOS/applet


Repeatedly seeing the following in console:

… com.apple.launchd.peruser.501[150] (com.mahogany.sarah[1156]): Job failed to exec(3). Setting up event to tell us when to try again: 2: No such file or directory
… com.apple.launchd.peruser.501[150] (com.mahogany.sarah[1156]): Job failed to exec(3) for weird reason: 2
… com.apple.launchd.peruser.501[150] (com.mahogany.sarah): Job should be able to exec(3) now.


So, I am concluding that the file is not referenced correctly. 

In case it helps, the plist file in ~/Library/LaunchAgents looks like:

&lt;dict&gt;
    &lt;key&gt;Label&lt;/key&gt;
    &lt;string&gt;com.mahogany.sarah&lt;/string&gt;
    &lt;key&gt;ProgramArguments&lt;/key&gt;
    &lt;array&gt;
        &lt;string&gt;~/Applications/Trans_Helper.app/Contents/MacOS/applet&lt;/string&gt;
    &lt;/array&gt;
    &lt;key&gt;StartCalendarInterval&lt;/key&gt;
    &lt;dict&gt;
        &lt;key&gt;Hour&lt;/key&gt;
        &lt;integer&gt;15&lt;/integer&gt;
        &lt;key&gt;Minute&lt;/key&gt;
        &lt;integer&gt;25&lt;/integer&gt;
    &lt;/dict&gt;
&lt;/dict&gt;


EDIT: It finally worked using suggested changes AND removing the tilde from before /Applications. (This is, incidentally, exactly what the Finder > File Info displays for the applet)

&lt;dict&gt;
    &lt;key&gt;Label&lt;/key&gt;
    &lt;string&gt;com.mahogany.sarah&lt;/string&gt;
    &lt;key&gt;Program&lt;/key&gt;    // Change here and removing 1st char of string on next line
    &lt;string&gt;/Applications/Trans_Helper.app/Contents/MacOS/applet&lt;/string&gt;
    &lt;key&gt;StartCalendarInterval&lt;/key&gt;
    &lt;dict&gt;
        &lt;key&gt;Hour&lt;/key&gt;
        &lt;integer&gt;15&lt;/integer&gt;
        &lt;key&gt;Minute&lt;/key&gt;
        &lt;integer&gt;25&lt;/integer&gt;
    &lt;/dict&gt;
&lt;/dict&gt;
There's two problems with the above plist.


You've put the program in the ProgramArguments key.

Replace the ProgramArguments key with the Program key and the array with a string.
You can't use ~ in a Launch Agent plist.

Replace the ~ with the absolute path.