I need to add instructions that indicate to keep the jar shut tight or it will dry out. Pretty sure it is done for if it dries out. Since I did not think to add instructions I will send you another jar. I just realized that another student had this same problem. Jody, If you see this, email me and I will send you another one too.
I have kept many jars of this good for a very long time. I think you have to make sure the screw top threads of the jar are free and clear before shutting it tight.
On my glue jars I will add some petroleum jelly along the thread of the jar lid to make sure it doesn't stick and opens and closes smoothly.