I am trying to create a new SQL server agent alert to capture "SQLServer:General Statistics|Processes Blocked||>|5' but it looks like alert creation GUI is not able to see any perfmon counters as in the following picture:

The drop downs for Object, counter and instance are empty.
I can't even create the alert using TSQL as follows:
I can see these counters collecting data in perfmon.
Any ideas? Thanks in advance...