Ehrm... why would you create your databases on the D drive, but store your log files on the C drive?

Anyway, since you are using the simple recovery model you cannot take a log backup.

So you can either

* shrink the log file (not really recommended)

* allocate more space on the C drive (probably a temporary solution)

* move the log files to a bigger disk (the way to go)

Another question: why is the "ssisdb" creating log files?