English is not my native language so I may have difficulties to explain my case.
I am currently using RStudio for a Portfolio Management assignment in University. My problem is that I want to re-run the script I made last week and some codes don't work anymore (it gives me a NULL value) when I start them. Sometimes, when I just close my RStudio program and re-open it immediately after, the problem disappear. But the day after, I face the same problem. Moreover, I send the same script to a friend and he has no problem with codes when he runs them. It is quite annoying, can someone help me please ?