Hi Pankaj,
It is possible that you are seeing this error due to the fact the backend LDAP server is looking for missing value for first parameter in your filter and failing to do so, smps log is throwing this generic error of 'Wrong syntax of LDAP search filter'?
i.e. all examples in snippet you provided has filer with (samaccountname=) or (mail=).
If you compare this to what you found in published technical document (where the same error was reported for having a space... which obviously doesn't apply in your case), you will notice that every attribute that is part of a search filter has a value assigned to it.
I recommend try assign a value to 'mail' or 'samaccountname' and see if that makes any difference.
Thanks,
Hitesh