Why access point restarts on gpupdate?

Clarifications

...that's part of the reason that the 'force' option is supposed to be used 'for emergency only'.

Forcing the whole policy to be replaced uses a LOT of network traffic.

What type of AP is this? i would look for a configuration problem in the AP, such as a misconfigured ethernet uplink (wrong duplex settings), which is causing it to drop packets.

Ethernet configuration is ok, because other PC, which is connected to same AP, works ok when runining gpupdate. AP reboots also when policy is snchronized normaly. By our configuration it happens every 1.5 hours. Is it possible, if there is some policies or registry keys, that can be configured by GPO, that changes some informtion about wireless connection and if it's damaged and couses errors in AP. In result AP reboots.

Really an AP should not reboot no matter what you send through it, of course. I have been working with enterprise WLANs for many years and have never seen that.

Just for curiosity, I would hookup a PC with WireShark and connect via Ethernet hub between AP and LAN; then create a trace doing Gpupdate via wired and compare with WLAN gpupdate. I would guess there is something like a flood of malformed packets or some unreasonable number of authentication requests that are killing the AP. The AP is a mac-layer bridge, so it is logically no different than an ethernet cable, from a connectivity perspective.

That on same PC i've logged with different user, everything goes well. So i think there is'nt a problem in packet level. I've this problem with few users. One user i just removed from AD and recreated, the problem dissapears with that user. Then i assume that hardware level and protocol level is ok, then problem should be in user configurations. Is it right?

This error is D-Link related. I've solved this.

Correction, this is not really d-link related. In Active Directory enviroment for authentication Kerberos v5 is used. The problem is, that Kerberos uses UDP protocol and sometimes it sends big amount of data and in transport level get errors, thet causing access point to reboot. For me was solution to change registry keys in windows for bigger packets and force use TCP protocol.
Small instruction:
1. Run regedit
2. Expand HKLM\System\CurrentControlSet\Control\LSA\Kerberos\Parameters (if Parameters does not exist, then just create it)
3. Create DWORD value with name MaxPacketSize and modify value 1 (decimal)
4. Create DWORD value with name MaxTokensize and modify value 65535 (decimal). This changes packet size (in Windows default value is 12000).
5. Restart PC.
6. Try again run gpupdate or other program, wich causing ap reboot.

I hope it helps.