Octopus Deploy integration with F5

Hi,

Using the "F5 - Enable, Disable, or Force Offline Member with optional wait for connections to drop" step in Octopus, I'm trying to disable a member in a pool.

The disabling itself works, but the "get_statistics()" call to determine when there are no more active connections to the member is failing.

The code:

$pool_name = "path to my pool"
$member = "member:port"
$vals = $member.Split( (, ':'));
$member_addr = $vals[0];
$member_port = $vals[1];
$MemberDef = New-Object -TypeName iControl.CommonIPPortDefinition;
$MemberDef.address = $member_addr;
$MemberDef.port = $member_port;
$MemberDefAofA = New-Object -TypeName "iControl.CommonIPPortDefinition[][]" 1,1
$MemberDefAofA[0][0] = $MemberDef;
$F5.LocalLBPoolMember.get_statistics( (, $pool_name), $MemberDefAofA);

The error:

Exception calling "get_statistics" with "2" argument(s): "Exception caught in
LocalLB::urn:iControl:LocalLB/PoolMember::get_statistics()
Exception: Common::OperationFailed
primary_error_code : 16908336 (0x01020030)
secondary_error_code : 0
error_string : "
At line:19 char:1
+ $F5.LocalLBPoolMember.get_statistics( (, $pool_name), $MemberDefAofA) ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : SoapHeaderException

We're running BIG-IP 12.1.2.

Any help or advice will be greatly appreciated!

Thanks, Sean