cannot focus a disabled or invisible window错误

                            
各位大哥   
   我写了一个Delphi+SQL的成绩管理系统,可运行的过程中经常出现"cannot   focus   a   disabled   or   invisible   window"这个错位提示.   
   请问这是什么意思,怎么样去除这个错误?

                                

• ·怎么造成Cannot focus a disabled or invisible window.这个错误？
• ·why cannot focus a disabled or invisible windows?
• ·关于'Can not focus a disabled or invisible window'的错误？
• ·Delphi运行时的问题，cannot focus a disabled or invisible window！
• ·大们救命阿!!! 为什么会有Cannot focus a disabled or invisible window 的错误？ 500分求解！！！！！ 十万火急急啊！！！
• ·我的软件，子窗体用ALT+F4关闭，出现“CanNot focus a disabled or invisble windows”请问是什么意思？
• ·关于adoquery1的错误 Cannot perform this operation on a closed dataset
• ·在dll里点DBLookupCombo时出现"cannot assign a tfont to a tfont"的错误
• ·为什么我一ShowModalForm(FRM)，就抱'Canot make a visible window Modal'错误
• ·MDI窗体,打开子窗体出现问题~提示:Cannot make a visible window modal
• ·我想用timer组件实现自动登陆,怎么老提示cannot make a visible window modal,40分请教
• ·创建模态窗体的奇怪问题！提示“Cannot make a visible window modal.”
• · Cannot assign a TFont to a TFont
• ·cant make a visible window modal
• ·query.edit出现了cannot modify a read_only dataset的错误是为什么呢》》
• ·急，为什么我一ShowModalForm(FRM)，就抱'Canot make a visible window Modal'错误
• ·我在DLL中建立了一个TImage,但调用时出现错误"Cannot assign a TFont to a TFont"
• ·[dll问题] 错误为“Cannot assign a TFont to a TFont” 相亲请进->
• ·Cannot perform this operation on a closed dataset!!
• ·cannot perform this operation on a closed dataset!