Issues creating report...
What issues? It helps us offer suggestions if we have an idea of what you're trying to do and what you think is wrong.
First thing I see is that you didn't END your CASE. Without that, the query doesn't run at all.
One possible problem I see is that, because you're reporting on all active assets but only checking the state of one model (or however many specific models you end up checking), everything outside of that list of models is being reported as "patched" even though you haven't checked them. If it were me, I'd constrain things, limiting the output to only the models being checked, e.g.
Where
tblAssetCustom.State = 1
AND tblAssetCustom.Model In ('Latitude E5540', 'Model 1', 'Model 2')
Alternatively, you might consider checking for both patched and unpatched values and leave the ELSE as a fall-through for anything you haven't checked, e.g.
Case
When tblAssetCustom.Model = 'Latitude E5540' And tblBIOS.SMBIOSBIOSVersion < 'A21' Then 'Needs Patch'
When tblAssetCustom.Model = 'Latitude E5540' And tblBIOS.SMBIOSBIOSVersion >= 'A21' Then 'Patched'
When tblAssetCustom.Model = 'Model 1' And tblBIOS.SMBIOSBIOSVersion < 'A21' Then 'Needs Patch'
When tblAssetCustom.Model = 'Model 1' And tblBIOS.SMBIOSBIOSVersion >= 'A21' Then 'Patched'
When tblAssetCustom.Model = 'Model 2' And tblBIOS.SMBIOSBIOSVersion < 'A21' Then 'Needs Patch'
When tblAssetCustom.Model = 'Model 2' And tblBIOS.SMBIOSBIOSVersion >= 'A21' Then 'Patched'
Else 'Not checked'
End As BiosPatched
You should also bear in mind the the BIOS version is stored as a string, so you'll be doing ASCII-betical comparisons. If all you're dealing with is "A00"-format values, it's not a big deal, but if a machine has BIOS version 1.9.3 and the latest is 1.10.7, "1.9" is greater than "1.1" so you'll need to be craftier about handling the possibility. (I only bring it up because I see from my inventory that Dell has moved from the "A00" format to "x.y.z" on newer machines.)