I get the subject error with the ITSM 3.0.5 version. Same error 
ocurred with 3.0.3 version, that's is the reason why I upgraded to 
3.0.5, but the error still continues.
When I select "new" at the CMDB menu and I choose a class of CI, I get 
an Ajax error, when I accept to see the complete error I get this 
message:

----------
ITSM.Agent.CustomerSearch is undefined

(?)()@https://otrs.mydomain.com/otrs/index.pl?Action=AgentITSMConfigItemEdit;ClassID=33:755
Ready((function (j, s) {return new b.fn.init(j, 
s);}))@https://otrs.mydomain.com/otrs-web/js/js-cache/CommonJS_534d7e277cf7c791de931cd911c0d099.js:582
trigger()@https://otrs.mydomain.com/otrs-web/js/js-cache/CommonJS_534d7e277cf7c791de931cd911c0d099.js:37
trigger([object 
Event])@https://otrs.mydomain.com/otrs-web/js/js-cache/CommonJS_534d7e277cf7c791de931cd911c0d099.js:37
--------------

After the error occurs the window gets blocked and I can't save the CI.

If someone can help me, I'll appreciate it.
Thanks.