Problem with estimated position PROG page

Good day everyone,

My name is Lucas, I am from Argentina and I have downloaded FSX from Steam and purchased A320 from Aerosoft.

i’m having troubles with estimated position in PROG page, once I start flying position diverts to enormous values like 10 or 20 nm over the required one leading on huge dificultes to fly RNP approaches or even trying to fly any type of FPA app due to lack of positioning from FMCG.

I hope you can understand my issue and I apologize if this was already sales, I couldn’t get to find any response through the searcher.

Thanks