What we mean is make sure each file is only one contract and not several contracts lumped into one .pdf file. You do not have to wait until a contract has been transcribed before doing the next one.
And we're sorry about the error! We're still in beta testing, so we'll be sure to look into it! If you could, try the upload again, and if doesn't work, post the error message, or email it to me (firstname.lastname@example.org).