Ah, ok.
You can get around that error by using a Block Until Done tool in front of your 3 outputs that write to the same file. You can put it anywhere upstream that makes sense, but for efficiency should go as close to the output tools as possible.
The Block Until Done tool has 3 outputs, so make sure you connect the 3 streams to the different outputs of the Tool.
Why do you need to do this with the new driver? Because the Legacy driver will happily write to the "open" Excel file while we will not.
Microsoft is using an additional library that allows Excel files to be written to if open by a Microsoft product (for example, Excel itself or the Access driver).
So, if the file is currently open, the Access Driver will use the additional runtime library to do the write into the open Excel file.
The thing to understand is that some functionality differs between the two (Access Driver vs Runtime Library), so you can actually get different data out depending on whether the file was open at the time or not.
The differences that we've noted as well as reported by users effects datatypes that can be rounded. The Access Driver has different rules than the runtime library, so the resulting data can potentially be different.
If an Excel file is open in Excel, or by the Access Driver, then Alteryx will not be able to write to it. At the file system level, Excel and the Access Driver both open with a write lock.
Similarly, when we open a file for write, we also open it with a write lock which will not allow another process, such as another stream in Alteryx, to write to the same file.
Hence the Block Until Done Tool - which serializes downstream processing. Each sheet will write in turn and the next won't start until the previous stream has finished and closed the file.
Hopefully this information is useful.
