Trouble with showing a error message. Is there a size limit?

I have some code that inserts data into a table. There is an error that occurs and I want to show the error to the user. All my SQL code is in seprates classes and the return of the function is a boolean.
In my code behind I normally show a error like this.
 
strmessage = "Failed to update the Printer list. " & Session("error") ScriptManager.RegisterClientScriptBlock(Me.Page, GetType(Page), "clientScript", "alert('" & strmessage & "')", True)  
I have palced the error message into a Session variable that I then append to the strmessage variable as shown above. The issue I have is that when I run the code the error occurs but the messagebox never shows. The only thing I can figure is that either there is a character in the strmessage that screws up the scriptmanager or the error message is too long.
Here is the message that should show in the message ...