hi peter
I faced a general error with no further information in photoshop cc when I used your code for a try, even there was no save as dialog box.
for me it helped to declare the destination path as string.
tellapplication "Adobe Photoshop CC"
settheDocumenttocurrent document
setmyFileto "System:Users:imac7:Desktop:MH.jpg" asstring
setmyOptionsto¬
{class:JPEG save options, embed color profile:true, quality:12} ¬
savetheDocumentinfilemyFileasJPEGwith options¬
myOptionsappendingno extensionwithoutcopying
endtell
hope this helps.
have fun.