Relinking Problems "targets of an incomplete render...'

[DAEerror]

Hello,

I'm having trouble with some files that I am unable to relink. The files are being used in a number of sessions and while this works for the majority of files in some cases it seems impossible to relink. Whenever I boot up a session the files are offline and it does not give me the option to relink them in the relink page. If I close this and go to the session browser and try and manually relink the selected files I get the error message;
'targets of an incomplete render cannot be relinked'
Has anyone come across this message and know why it might be occurring?

Many thanks in advance
Alistair