How to fix W3WP error happening in IIS while generating Crystal report and downloading in binary format

I'm trying to generate crystal report in server using WCF and downloading in binary format to client machine. Service is calling from wpf application in loop.It will generate report for some records and then it will throw the w3wp. exe error. I monitored the error using Debug Diag tool and got a following summary in log

|---------------------------------------------------------|
| Count | Exception                                       |
|---------------------------------------------------------|
| 1926  | System.String                                   |
| 41    | 0XE06D7363                                      |
| 2     | System.AppDomain                                |
| 2     | System.InvalidOperationException                |
| 2     | System.Threading.QueueUserWorkItemCallback      |
| 1     | 0XE0434F4E                                      |
| 1     | CrystalDecisions.Shared.CrystalReportsException |
|---------------------------------------------------------|

I'm not able track the correct cause of error?