The "save as" button? ... is this when you have two files of the same name? If you use this feature it is possible that Lmewire will freeze for up to a minute or so (I find this using an old Mac model) I suggest just waiting few minutes and checking if LW will actually sort it's self out and I think you will find it will .. It may just be a case of taking a short walk and being patient.
If ths is no help let us know some system details... Platform OS Processor speed RAM Free space .... and Java and Limewire versions (see Limewire Help>about ...)