Can't connect to MC42FS

I am having problems connecting to a MC42FS.The PLC worked fine last friday but when trying to upload some weekend changes this morning the PLC suddenly stops working. On the first programing attempt after power-on the programing process stops at "stopping applications" followed by a "no handshake replay". Trying to program the PLC after will only result in a "no handshake replay". If connecting to the PLC after cycling the power with IQAN run i get the following error. "There is no valid application in the target module. Error code R4:2 1:1:1 (Int.diag error(Backending?)) MS42FS[NI address tag] (FW version 6.04.4) i have tried multiple times with and without the ID-tag, but nothing changes. Any ideas on how to get it working again?