Sometimes MS Excel locks certain files during installation, which can cause the Click to Convert button to not appear in Excel. Here are some steps to manually install the button:

1) Install Click to Convert.
2) Copy the file called "clicktoconvert.xla" which is where you installed Click to Convert - in the Office\XLStart folder (usualy C:\Program Files\ClickToConvert\Office\XLStart\)

Copy that file into one of the following locations - try looking for one of these three folders (you will only have one of the below):

1) Windows \ Application Data \ Microsoft \ Excel \ XLStart
2) Windows \ Profiles \<User Name>\ Application Data \ Microsoft \ Excel \ XLStart
3) Program Files \ Microsoft Office \ Office10 \ XLStart

Note: The "Windows" folder (mentioned above) may also be called WinNT instead.

Note: Replace <User Name> with the login name of the user who you wish to install the toolbar button for.