SUBVIEW.dll causing AccessViolation

Does anyone here encounter an error for the SUBVIEW.DLL? We created a WEB API, when deployed it is fine when creating single calls. But when doing multiple calls simultaneous we got w3wp.exe error. Upon analyzing the dump file it shows: \vi65a\SUBVIEW.dll has caused an access violation exception (0xC0000005). What are the subview?

Thanks,