How to deal with (ex-) supervisor not meeting promise to write reference letter Before actually submitting anything, I contacted one of my ex-supervisors and he agreed to write a reference letter for me. That was almost a month ago. Then, the first time he received the invitation to submit a reference for me (invitation self-generated from the online application system), he promised he will submit it "soon" with enthusiasm. 

However, days went by, after two weeks of the initial invitation, nothing was received. I therefore sent a reminder to him and he again said he will submit it in one to two days (he did mention he was a bit busy). Now a week has passed and still nothing. The deadline for getting the reference is closing soon (in two weeks).

What should I do? I have options to send him an email reminder personally (I cannot call him because we live in different countries right now). Or I can re-send an invitation via the application system. Which one would be more polite, as well as more effective in getting him to actually write it?
I'll guess you have done about all you can other than send a final notice very close to the deadline. The prof is probably targeting that "drop dead" date and continuous reminders may just get in the way. But a note on the next to last day would be good. 

You might also start to think about other options. Who else might be able to do this for you?