Login to the SAP System and opening a new modus takes too long

Hello friends

I have a problem on my SAP ECC 6.0 system. When some users (but not all users) try to login (via SAPGUI) or open new modi this takes within 5 minutes to happen. I have allready excluded local hardware problems on the client PCs (You can logon on the same computer with another user without having that delay).

In Sapgui the Option "Extras - Settings - Do not display picture" is already set.

Could anyone give me a hint please in which direction I could search for the solution? This would be very helpful.

Thanks a lot in advance!

Greetings

Marco