First, thanks for the answer.
I doesn't use any Antivirus or at least it's totally off. Also the Windows Firewall is off. I only use Kaspersky from time to time to scan my whole PC.
In the meanwhile, I used "http://n1.netalyzr.icsi.berkeley.edu" to test everything. The result is, without any upload with F&IU I get no red errors etc., but with running uploads I get those red errors:
- Direct TCP access to remote SMTP servers (port 25) succeeds, but does not return the expected content.
- Direct TCP access to remote DNS servers (port 53) is blocked.
- The network you are using appears to enforce the use of a local DNS resolver.
- Direct TCP connections to remote POP3 servers (port 110) succeed, but do not receive the expected content.
- Direct TCP connections to remote RPC servers (port 135) succeed, but do not receive the expected content.
- Direct TCP connections to remote NetBIOS servers (port 139) succeed, but do not receive the expected content.
- Direct TCP connections to remote IMAP servers (port 143) succeed, but do not receive the expected content.
- Direct TCP connections to remote SNMP servers (port 161) succeed, but do not receive the expected content.
- Direct TCP connections to remote HTTPS servers (port 443) succeed, but do not receive the expected content.
- Direct TCP connections to remote SMB servers (port 445) succeed, but do not receive the expected content.
- Direct TCP access to remote SMTP/SSL servers (port 465) is blocked.
- We are unable to deliver non-DNS UDP datagrams to our servers.
- The time it takes for your computer to set up a TCP connection with our server is 3200 ms, which is quite high.
All this was green without any uploads. So it might be my router, I think. I got a new one about 2 weeks ago and never uploaded anything from then until now. So now I used F&IU again and noticed this problem first. In the end, the problem is probably NOT F&IU, but some config shit from the new router.
Maybe someone can give me a hint or something, what could be the problem? It only happens with uploads, as far as I can see. I don't use any other filesharing stuff at the same time (but they worked flawlessly all together months ago, if you ask). I'm a bit confused here...