Templates timeline_cell_class + Ajax call + IE =problems

Hello
I am great difficulties with the timeline_cell_class templates.

I am trying to display in each cell a different color if my unit is available or not.
To know if it is available I call a webservice that send me the information for the day (this unit can be available or not, and if available, I can have up to 3 periods of time where he is available).

My first try :

scheduler.templates.timeline_cell_class =function(event_list,time,ressource_timeline) {
   if(ressource_timeline.id_codcal!='') {		 
      return "AVAIL";  
   }   
   else
       return "NOTAVAIL";
}

With this simple code no problems in IE or firefox. If the id_codcal have a value it available and else it is unavailable.

but with the following :

scheduler.templates.timeline_cell_class =function(event_list,time,ressource_timeline) {
   if(ressource_timeline.id_codcal!='') {
      $.ajax({ url: varurl+"CalAvailability",   
 	      dataType: 'json',   
	      data : $.param({'ID_CODCAL': ressource_timeline.id_codcal,'DAY':time.getDate(),'MONTH':time.getMonth()+1,'YEAR':time.getFullYear()}),   
                   async: false});  
      return "AVAIL";  
   }   
   else
      return "NOTAVAIL";
}

This webservice sends back a json object containing the information I would like to test (available or not, and the differents hours of availibility).
I have removed the unnecessary code, as the simple fact to add the ajax call seems to lose IE completely.
If I try in firefox it is OK, the code is completed with sucess.
But in IE, it seems to go in some kid of deadlock as I usually have to call the task manager to kill the task.
Note that I don’t even try to do something with the result I just try to have my result (as I have tried to advance a bit more with forefox I have done something to put the result of my calls in a array so that I don’t have to launch the ajax call for each cells, I tried with IE after having completed the work in firefox but the problem is the same)

Am I doing something wrong (it seems to me that as it works with success with firefox, it should be ok), but…

Thanks in advance for your help.

The code itself looks fine, problem can be in count of request - currently you are executing request for each cell of timeline , and there are a lot of cells - which results in massive swarm of ajax calls.