Close LW & restart the program. Recent LW versions have had problems with being in queued/busy mode or pause mode. If necessary re-search the topic of the file so it can find sources to make sure the file is 100% downloaded or verified as being ok.
I've personally found files in queued mode need to be Resumed to become active on occasions. O.o Which means LW is not double-checking the files frequently enough to be sure they can in fact connect but go into a state of infinity of queueing which is 'poor' programming on LW's part; LW bugs.