Hi Khalid,
You can do the following to turn single user mode on/off
USE master
EXEC sp_dboption 'yourdb', 'single user', 'TRUE/FALSE'
To why this is automatically happening I'm not sure, maybe you could post some of the log details.
Laters
*I didn't do anything it just got complicated*
"I didn't do anything it just got complicated" - M Edwards