eConnect error 647 - taRMTransaction

SQL error occurred inserting into the RM Keys Master Table - RM00401, sometimes you will get this error when you are calling the eConnect method taRMTransaction.
This issue could occur if you’re trying to create a AR document (Invoice , Debit Memo) and on same time you are trying to collect the cash on fly (cash type =Check) as per eConnect functionality user can collect the cash directly in the AR document (Invoice , Debit Memo) by providing the following details:
1. Check Amount        
2. Check Number                
3. Checkbook ID Check                                                 
4. Check Date
5. Document Number Check         
This issue could occur because Document Number Check / RMDTYPAL=9 (Cash) which system pass to  eConnect has document already exists RM Keys Master Table, there could be many reasons behind this issue e.g. if you are calling eConnect or any other script to generate the Check document number and if this script failed to update the next document number properly you will end with this issue.
As solution before you call the taRMTransaction. you need to verify the Check document number which you passing to eConnect and if the document number already exists in RM00401 then you can get another document number, also you can through an error in the integration process and you can investigate more behind this issue.