Issue in confirmation of putaway WT with Serial No

I have a serial no managed material. ERP IBD created with manually entered SNs. EWM IDN and ID are created.

ID item details has the SNs which I entered in ERP IBD. Putaway WT was automatically created.

While confirming the WT, when I select Serial Numbers Actual button, it shows up the SNs I desired.

I just select these 2 SNs and proceed for confirm+save, system gives me the error as follows.

what is issue with the serial no? I checked /SCWM/SERH.. it has not any entries created yet.

Thanks.