Gmail Unable to upload because it is a folder or a package (like an application bundle or RTFD document)

You get this error message because you just tried to attach a folder/directory which is not allowed. You need to use a compression tool to generate either of .zip, .tar, .tgz, .taz, .z, .gz or .rar of the folder ( If you are on Mac OS X, simply right click of the directory and Select Compress .

Note following files within a compressed file are not allowed :

.ade, .adp, .bat, .chm, .cmd, .com, .cpl, .exe, .hta, .ins, .isp, .jar, .jse, .lib, .lnk, .mde, .msc, .msp, .mst, .pif, .scr, .sct, .shb, .sys, .vb, .vbe, .vbs, .vxd, .wsc, .wsf, .wsh

Read more : https://support.google.com/mail/answer/6590?hl=en