I tried exactly what you did again in 2016.1 and did NOT get the errors you see.
Regarding your claim to know the proper syntax with
plot(t,x=0..2) let me remind you that YES that is BAD syntax. With that you WILL get the errorWarning, expecting only range variable x in expression t to be plotted but found name t
That error is received in both 2016.1 and in Maple 18. Again bad plot syntax as I correctly suggested earlier. Considering you most likely mistakenly forgot about that bad syntax you presented I could not no matter how hard I tried to get the error you presented.
Your bugs in parsing resource can not be found. It is most likely some combination of lines you deleted and re-executed after which caused the error. Maple integrates no problems for me with Pi and pi in the definite integrals. As with differentiation, it is carried out with no problems.
int(x^2,x=0..2) returns the correct answer.
using the graphing interface I tried multiple times to replicate your error.
Let me ask if you have been able to repeat your errors on a new sheet?