Hi, I hope someone can help me

I have the following formula and as I step through it, I can't see any
problem with it, however it keeps returning an error.

Rolls!A4 contains the following formula

=INDIRECT((VLOOKUP(B2,D41:F50,3,TRUE))&"!")&A5

What I am trying to achieve:
I have 10 worksheets with a list of students names on each. the Vlookup
formula refers to an index [D41:F50] containing the following information:
className Teacher sheet
Eg. 9ISTX Mrs Duffy 1

Any assistance would be appreciated.
Regards
tanya