[ZBX 2.2] powershell & system.run

[eljibe]

I'm trying to monitor a log file.
The host through which I access it is a "Cluster Access Point". Which means I have an agent installed with this configuration:

Hostname=WindowsClusterNode

And the host, in the Zabbix GUI, is named WindowsClusterAccessPoint.
So no possibilities to use the builtin logfile monitor of the agent.
So I'm trying this, in powershell:
count the number of occurences of a string in a file.
From the CMD, directly on the machine, I can achieve it like this:

C:\Users\me>powershell -Command "$f=Select-String -path d:\jbw\liste.txt -pattern 301 -allmatches; $f.count"
1658

I can also make it work properly using a more complex pattern:

C:\Users\me>powershell -Command "$f=Select-String -path d:\jbw\liste.txt -pattern "301, party" -allmatches; $f.count
1658

Using this with zabbix_get, it works:

[root@ZBXSRVR]# /opt/zabxagent/bin/zabbix_get -s ZBXHOST -k system.run["powershell.exe -Command \"\$f=Select-String -path d:\jbw\liste.txt -Pattern 301 -AllMatches; \$f.count\""]
1658

BUT if I try this with a more complex pattern, I get this:

[root@ZBXSRVR]# /opt/zabxagent/bin/zabbix_get -s ZBXHOST -k system.run["powershell.exe -Command \"\$f=Select-String -path d:\jbw\liste.txt -Pattern \"301, Called party identification not known\" -AllMatches; \$f.count\""]
ZBX_NOTSUPPORTED

I have tried using a variable, with no more success.

[root@ZBXSRVR]# pattern="301, Called party identification not known"
[root@ZBXSRVR]# /opt/zabxagent/bin/zabbix_get -s ZBXHOST -k system.run["powershell.exe -Command \"\$f=Select-String -path d:\jbw\liste.txt -Pattern ${pattern} -AllMatches; \$f.count\""]
ZBX_NOTSUPPORTED
[root@ZBXSRVR]# /opt/zabxagent/bin/zabbix_get -s ZBXHOST -k system.run["powershell.exe -Command \"\$f=Select-String -path d:\jbw\liste.txt -Pattern \"${pattern}\" -AllMatches; \$f.count\""]
ZBX_NOTSUPPORTED

I am running out of ideas.

My file looks like this:

random line
301, Called party identification not known
301, Called party identification not known
another random line
yet another random line
another random line
301, Called party identification not known

if anyone had an idea, I'd gladly take it.