dbWriteTable does not append rows in database

Hi List,
I want to append some rows from R into sql server. So, I submitted the code below. there is not any error message:
dbWriteTable(conn = con,?name = "PMDB._Alias_A", value = try1, overwrite=FALSE, append=TRUE, row.names = FALSE)
But when I try to query the data from the Sql server, I can not find the records were appended. Did I miss something in the code?
Thank you,
Kai