We got caught with this error recently when built a new BizTalk server. Every time we tried to browse to the web portal we got a 503 error and the application pool would stop. We could restart the app pool without error. It took us a while to work out the root cause. We checked a lot of things and proved that all other web services worked without any problems.
Eventually we discovered the following error most easily seen on the web server roles page.
The error was ;
“The identity of application pool BAMAppPool is invalid. The user name or password that is specified for the identity may be incorrect, or the user may not have batch logon rights. If the identity is not corrected, the application pool will be disabled when the application pool receives its first request. If batch logon rights are causing the problem, the identity in the IIS configuration store must be changed after rights have been granted before Windows Process Activation Service (WAS) can retry the logon. If the identity remains invalid after the first request for the application pool is processed, the application pool will be disabled. The data field contains the error number.”
The IIS user group had not been granted “Log on as a batch job properties” under the local security policy. Once this was corrected the BAM portal now displayed without error. Thanks to Mike Laughton and Shadab Anwer solving this problem.