matlab 7.0绘制根轨迹图时出现如下问题,开始还好好的,但之后却出现这个问题（程序一定没问题）.

matlab 7.0绘制根轨迹图时出现如下问题,开始还好好的,但之后却出现这个问题（程序一定没问题）.
a.m内容是
G=tf([1 4],[1 4 20]);
figure(1)
pzmap(G);
figure(2)
rlocus(G);
以下是运行后的问题!
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The element type "name" must be terminated by the matching end-tag "".
Could not parse the file: d:\matlab7\toolbox\ccslink\ccslink\info.xml
>> a
Warning: File: D:\matlab7\toolbox\control\control\@lti\private\gainrloc.m Line: 148 Column: 22
The expression on this line will generate an error when executed. The error will be: Attempt to execute SCRIPT j as a function.
> In lti.genrlocus at 59
In resppack.ltisource.rlocus at 22
In wavepack.waveform.draw at 21
In wrfc.plot.draw at 18
In wrfc.plot.init_listeners>LocalRefreshPlot at 87
In lti.rlocus at 94
In a at 5
Warning: File: D:\matlab7\toolbox\control\control\@lti\private\gainrloc.m Line: 152 Column: 24
The expression on this line will generate an error when executed. The error will be: Attempt to execute SCRIPT j as a function.
> In lti.genrlocus at 59
In resppack.ltisource.rlocus at 22
In wavepack.waveform.draw at 21
In wrfc.plot.draw at 18
In wrfc.plot.init_listeners>LocalRefreshPlot at 87
In lti.rlocus at 94
In a at 5
? Error using ==> @lti\private\gainrloc>initgain
Attempt to execute SCRIPT j as a function.
Error in ==> wrfc.plot.init_listeners>LocalRefreshPlot at 87
draw(this)
? Error occurred while evaluating listener callback.