Can not add products to buy X get Y

When I create one promotion of buy X get Y, I can not add this product to coupon. I chose the product and Add, then click the Save button. After finishing, i click this coupon to view again, I did not see products has been added to the previous. What happened?
My Joomla version 1.5.20
VirtueMart version 1.1.5 stable

Hello,

Were you using AwoCoupon 1 free previously? AwoCoupon 1 Pro is different for adding products. You would need to double click the product and make sure it gets added to the list below. Also you might want to clear your browser cache so you are not loading any old javascript files from the free version.

I have tried many ways, I deleted all cache, cookies and history data, using many different browsers, different machines, but it's still not working. Is this because I had previously installed the AwoCoupon 1 free version, how to delete all of the data of AwoCoupon 1 free version i has installed before?

Hello,

It sounds like there might be a jquery conflict in your system. Do you have jquery loaded in the backend through a plugin? If so, disabling it for AwoCoupon should fix the problem. If you like I can look at it if you send me a private message with temporary admin access.