error creating site from template "non-supported field type change"

We customized a team site, adding lists and fields, etc, and then did a "save as template" - I'm trying to create a site based on that that template in another site collection. When I try to create a site based on that template I get an error "non-supported field type change. The field cannot be changed to the new type".  (this error also occurs when I try to create a new site from that template in the original site collection)

After much research, I output (using powershell) the field types from all the lists in the original site and also all the Site Columns in the site collection and compared them - I found that the customized site has a field named "Category" which has a different column type ("Choice") than the site column named "Category" (type="Single line of text")

I tried deleting the "Category" site column in a test site collection and then creating a site from the template, but still got the same error.

I've extracted the .wsp file, and I can see in the ListInstances\ElementsFields.xml where the Category field is 'redefined' to be a choice field

<Field ID="{6df9bd52-550e-4a30-bc31-a4366832a87d}" Type="Choice" Group="_Hidden" Name="Category" DisplayName="Category" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="Category" Overwrite="TRUE"><CHOICES><CHOICE>(1) Category1</CHOICE><CHOICE>(2) Category2</CHOICE><CHOICE>(3) Category3</CHOICE></CHOICES><Default>(2) Category2</Default></Field>

And there is another 'redefinition' of that field ID in the file ListInstances\Files\Lists\PMO Calendar\schema.xml   ("PMO calendar" is one of the lists in the site)

<Field ID="{6df9bd52-550e-4a30-bc31-a4366832a87d}" Type="Choice" Group="_Hidden" Name="Category1" DisplayName="Category1" SourceID="http://schemas.microsoft.com/sharepoint/v3" StaticName="Category1" ColName="nvarchar6" RowOrdinal="0">
 <CHOICES>
  <CHOICE>(1) Category1</CHOICE>
  <CHOICE>(2) Category2</CHOICE>
  <CHOICE>(3) Category3</CHOICE>
 </CHOICES>
 <Default>(2) Category2</Default>
</Field>

The fieldID show above is the same ID as the site column named "Category", which is of type "single line of text"

When I examine all the lists in the original site, there are 2 that have a field named "Category" with field type "Choice" - they are named "All Projects -Issues and Actions" and also "PMO Calendar"

Are there any suggestions for how I can adjust the xml in the .WSP file so that I can successfully create this site?

Thanks