This issue will occur during a constituent merge when you are attempting to merge a constituent that has been added as a bank in Altru. If the constituent that has an active bank account in Altru is set up as the source constituent Altru will show an error message. To resolve this issue make the Constituent that has been added into Altru as a bank the target constituent in the merge. 

To find out if a constituent has been added to Altru as a bank:
  1. Click Constituents > Constituent Search
  2. Search for and select the Constituent
  3. Check the Constituent record to see if there is a bank tab with account information User-added image

Before merging the two constituents you may want to check with your organization to confirm that this constituent should be merged as these records are setup in Altru during initial implementation.