Hello Karen,
As mentioned by others previously, your 'outfile=' path is wrong (it does not exist).
You can also search / screen this communities site for the same error message (the one you encounter). Several (students) before you have stumbled upon this 'issue'.
Anyway, not only your 'outfile=' option is wrong, also the 'data=' option is wrong!
SAS expects a libname.datasetname specification after 'data=' or just datasetname if the libname equals WORK.
Once your 'outfile=' problem is solved, you will get another error, something like:
ERROR: Libref acc_2012 is not assigned.
What you need is (probably):
proc export data=work.acc_2012 outfile='<<valid path>>/acc_2012.dta; run;
Do not forget to terminate your statement with a semicolon (;) and to terminate your proc export with a 'run;' statement.
Cheers,
Koen