<xsl:variable name="keyName"><xsl:value-of
  select="substring-after(../../ViewKey, ';')"/></xsl:variable>

It's better to go


<xsl:variable name="keyName" select="substring-after(../../ViewKey, ';')"/>

As it;s shorter and makes keyName into a string rather than a result
tree fragment containing a root node containing a text node.

But that doesn't make any difference to your problem.

<xsl:apply-templates select="//appInfo[ViewName='viewName' and
ViewKey=$keyName]/Structure[@StructId='VFM']/Row[@DEPEND='001']" >


That looks OK although anything with // in it is likely to be
inefficient and quicker if replaced by a call to key().

The usual cause of problems in this area is that the <xsl:variable 
isn't being evaluated where you think it's being evaluated:
stick
<xsl:message>
 keyName = ,xsl;value-of select="$keyName"/>
</xsl:message>
just before the apply-templates and see if it has the value you expect
(ie the value you said you used as a literal string)

David

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