I am getting this error too, but only upon uploading certain files. Some go through just fine, while others won't. I don't think it's a size issue, because I've uploaded a zip file larger than the one that is causing this error.
I've just installed my first plogger3 and experienced these issues. It was entirely down to file size. What I believe happens is as follows:
1. You upload a file (or archive containing a file) larger than allowed by the host server. 2. The host server ignores the file (thus it doesn't get saved to disk). 3. Plogger receives a list of uploaded files (including the name of the file that doesn't exist on disk because it was too big). 4. Plogger tries to access the file and bam, it can't find it.
By shrinking the files so that they were under the limit, this issue went away. However, as I run my own server, I just upped the limit - much better :)
I had the same problem and I've traced it to the file extensions being in uppercase. The upload seems to work if I change the the extension to lowercase.