Access CHarts

I have two problems

One: I am producing a line graph but on occasions some
lines are not always joined, ie.

if i have jan feb mar, and a value in each column, the
grpah draws a line from each value displaying a trend, on
occasions the lines line jan to feb will not be drawn but
line feb to mar will be.

two: my report is run by a click of ab utton,
occasionally the report prints an old version of it, ie i
select product bmw, audi, vauxhall, next time i add saab,
next time i add ford but then it print the first graph
being bmw audi vauxhall, not the new one