Do you get the same error with:
(vlax-invoke-method vla 'getboundingbox 'a 'b)
And:
(vlax-invoke vla 'getboundingbox 'a 'b)
Pretty much the same error, although the last option is reported slightly differently. Ugh!
Command: (setq vla (vlax-ename->vla-object ent))
#<VLA-OBJECT 00000000475cb448>
Command: (vla-getBoundingBox vla 'MinPoint 'MaxPoint)
errorActiveX Server returned an error: Error loading type library/DLL
Command: (vlax-invoke-method vla 'getboundingbox 'MinPoint 'MaxPoint)
errorActiveX Server returned an error: Error loading type library/DLL
Command: (vlax-invoke vla 'getboundingbox 'MinPoint 'MaxPoint)
errorError loading type library/DLL