InvalidDestinationHost - how can I fix this error?

Hello, I do not know much of this programm - it always went well until now. When knitting to pdf the following error appears:

Could not fetch http://?/UNC/
HttpExceptionRequest Request {
host = ""
port = 80
secure = False
requestHeaders =
path = "/"
queryString = "?/UNC/"
method = "GET"
proxy = Nothing
rawBody = False
redirectCount = 10
responseTimeout = ResponseTimeoutDefault
requestVersion = HTTP/1.1
(InvalidDestinationHost "")
Fehler: pandoc document conversion failed with error 61
Ausf├╝hrung angehalten

How can I change the library? The programm isn't installed in http://?/UNC/ etc. but in System (C). So why does it try to fetch that destination? What does error 61 mean?!

Maybe I`'m completely wrong. I'm looking forward to reading your answers, dear R-Community.