Importing External Data Locks Source Workbook

I am importing external data to "Workbook A" from the source workbook, "Workbook B." Workbook A is set up to refresh every 15 minutes. Workbook B is shared. I am recieving an error saying either, the 'file is in use', or 'the file is locked,' depending on the senario.

Scenario 1:
1. I open A and enable data connections.
2. I try to open B, but receive the message: '(File location...) is in use. Try again later.

Scenario 2:
1. I open B.
2. I open A.
3. I go back to B to edit information.
4. When I try saving the information I get the following message: 'File is locked. Try the command again later.'

I need to be able to have A open and periodically refreshing. I also need to allow users unhindered access to B at the same time.