TCL error :Prerequisite operation not in progress (line ...

I agree. I do not think the rule will work if HTTP is disabled. Combine the rules and set it up to only continue if the first part is not true (if/elseif) or perhaps add "return" after disabling HTTP to stop processing the event.

Thank you for the suggestion about the combination of the iRules. At this moment the next iRule is in place :

when HTTP_REQUEST {

        if {[HTTP::uri] starts_with "/partinsert"} {
         if { [string tolower [HTTP::header Upgrade]] contains "websocket" }{
            log local0. "websocket detected"
            HTTP::disable  
            }  
        }
    else {
        HTTP::uri "/partinsert[HTTP::uri]"
        }   
    }

The goal is to insert a text like partinsert into the url if it is not there, because of tha mentioned solution 14814 HTTP has to be disabled if websocket is detected. However this solution keeps on giving me the TCL error if a webconnect header is detected. I would like to solve the error message. This error is displayed :

err tmm4[9434]: 01220001:3: TCL error: _plugin_rule_/Common/pluginasm  - Prerequisite peration not in progress (line 1)     invoked from within "HTTP::class asm"

Any suggestions ?

Looks like you may have ASM enabled on the VS, which would require HTTP profile. You could try disabling ASM as per below;

when HTTP_REQUEST {

  if {([HTTP::uri] starts_with "/partinsert") and ([string tolower [HTTP::header Upgrade]] contains "websocket")}{
    log local0. "websocket detected"
    HTTP::disable 
    ASM::disable  
  }  else {
    HTTP::uri "/partinsert[HTTP::uri]"
  }   
}

It did not do the trick, however after some extra testing I was able to avoid the TCL error. The solution was to disable HTTP:class before disabling HTTP. The order seems real critical. The rule looks now like below.

when HTTP_REQUEST {
    if {[HTTP::uri] starts_with "/partinsert"} {
         if { [string tolower [HTTP::header Upgrade]] contains "websocket" }{
           log local0. "websocket detected"
            HTTP::class disable
            HTTP::disable  
            }  
        }
    else {
        HTTP::uri "/partinsert[HTTP::uri]"
        }   
    }

Thank you all for helping me to get to this solution. Should you have remarks on the last solution, let me know.

As far as i know, it should be enough to disable asm. Since 11.4.0, websocket should work with enabled http profile.