I have a problem to connect dropbox

I use iPad 2, and I cannot connect the program, version 1.3.1, with my drop-box. Namely, when I am in window "documents" and click the symbol of Dropbox, I arrive at menu "DjVu Reader wants access to a folder of your Dropbox". I choose "allow", but nothing happens. When next time I click the symbol of Drop-box, the message is "your dropbox account has been unlinked".

Yours, Sergei

SergeiBorisovich about DjVu Reader, v1.3.1