Abap in Eclipse Logon to system fail

Hello,

i am new user of abap in eclipse.

i already installed abap in eclipse plugin.

When i want to create a new project , i have an error

Logon to system XXX failed (Connection to system "XXX" is currently not available)

so i dont know exactly why this error occurs , the user specified is already existing .

so if there is someone who can help me ,i will be thankfull.

thanks for help