Since yesterday, my Apache/PHP server began to log strange messages: Listed here are excerpts in the logs. error.log:

[Mon Sep 05 12:37:25 2011] [warn] (OS 64)The specified network name is no longer available.  : winnt_accept: Asynchronous AcceptEx failed.
[Mon Sep 05 12:37:25 2011] [error] [client 77.85.194.198] Invalid URI in request \xec\x18\rN\x03.\xe7\x8c\xe46Cg\x85\x1a\xab\xca
[Mon Sep 05 12:43:37 2011] [warn] (OS 121)The semaphore timeout period has expired.  : winnt_accept: Asynchronous AcceptEx failed.

access.log:

178.37.24.223 - - [05/Sep/2011:12:36:41 +0200] "\xe80'y\xecT\xe5\xb7+\xba\x94\x92\xe4\xe4\xd6\x01Q\"\xe9p\x94\xe3" 200 2977 "-" "-"
77.85.194.198 - - [05/Sep/2011:12:37:25 +0200] "\xec\x18\rN\x03.\xe7\x8c\xe46Cg\x85\x1a\xab\xca" 400 226 "-" "-"
213.87.136.107 - - [05/Sep/2011:12:38:09 +0200] ">R1\x83\xa6\xf5\"\xd3\xe6\x85" 200 2977 "-" "-"
68.10.170.135 - - [05/Sep/2011:12:39:23 +0200] "-" 408 - "-" "-"
89.137.238.149 - - [05/Sep/2011:12:39:46 +0200] "-" 408 - "-" "-"
81.85.202.246 - - [05/Sep/2011:12:41:06 +0200] "-" 408 - "-" "-"
184.164.16.92 - - [05/Sep/2011:12:43:10 +0200] "\x02\xe0\x9fQ\xa1\x89s\x8d\x04\x1f\xb3o\xbc2I\xc4\x1f`>\xfd\x8b&Z\xae\xc0>" 200 2977 "-" "-"
208.54.44.237 - - [05/Sep/2011:12:44:39 +0200] "Zv\xa2\x05\xda\xc9\xe3\x17\xff\x18\xea\xd0}s\x88\xb8\xd3\xf6a\xee\xd6\xad\xf7\x8f|yoU+'\x9c\xea\xb4V_\xc8\x1b" 200 2977 "-" "-"
41.78.80.112 - - [05/Sep/2011:12:44:48 +0200] "\xc9\xbf\xc3!{hv:\x84\x83\x03\xeb\x1d\xd0,\xb5" 200 2977 "-" "-"

This is just a development server, however i have permitted all access within the .htaccess file, so I'm not sure what's going on. Any idea?

It appears bots are attempting known weaknesses/exploits in your development server to locate any vulnerability.

You are able to ignore them if you want but for me, the best move is obstructing individuals Insolvency practitioners or restrict use of your development server.

As lengthy while you keep the Apache patched, there will not be considered a problem. They are known exploits that cyber-terrorist (usually via a botnet) are fitting every IP on port 80. It is not particularly targeted at the server, more a 'fire at will' attack, wishing someone runs a mature version of Apache which is proven to be vulnerable against such attacks.