Mysterious issues with reading text files from R in ArcGIS and Excel

It seems within the last ~3 months Ive been having issues with writing text or csv files from a R data frame.  The problem is multifold and it is hard to filter  out what is going on and where the problem is.  So, Im hoping someone else has come across this and may provide insight.

My current settings for R:
R version 2.15.2 (2012-10-26)
Platform: x86_64-w64-mingw32/x64 (64-bit)
locale:

[1] LC_COLLATE=Swedish_Sweden.1252  LC_CTYPE=Swedish_Sweden.1252    LC_MONETARY=Swedish_Sweden.1252 LC_NUMERIC=C
[5] LC_TIME=Swedish_Sweden.1252

attached base packages:
[1] tcltk     stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] adehabitat_1.8.11 shapefiles_0.6    foreign_0.8-51    tkrplot_0.0-23    ade4_1.5-1

loaded via a namespace (and not attached):
[1] tools_2.15.2

I am using Microsoft Excel 2010 and ArcGIS 10.1sp1 for Desktop

Basically, no matter what data frame I am working on, when I export it to a text file to be use in Excel or ArcGIS problems arise.  Im not sure if it is R or these other programs, maybe forums for ArcGIS might be more appropriate, but this problem only occurs when I use tables that have been produced from an R session.

When I try to open a text file in Excel, either I get an error message stating
The file you are trying to open is in a different format than specified by the file extension.  Verify that the file is not corrupted and is from a trusted source.
Followed by
Excel has detected that 'file.txt' is a SYLK file, but cannot load it.  Either the file has errors or is not a SYLK file format.  Click OK to open the file in a different format
Then the file opens


Otherwise, the file opens "fine" the first time through - and "looks" ok. I can't figure out what Im doing different between the two commands of write.table as they are always written the same:
write.csv(file, file = "D:/mylocations/fileofinterest.csv") or write.table(file, file = "D:/mylocations/fileofinterest.txt")
Sometimes I will try to add sep = "," or sep = ";" but these don't make a difference (which I didn't figure they would).

The other program I use is ArcGIS and bringing in a txt file from R is really messing things up as 2 new columns of information are typically added and date/time data is usually lost with txt files, but not with csv files.

For instance - a text file that looks like this in Excel:
     id       x       y                date    R1dmed    R1dmean R1error R2error
1 F07001 1482445 6621768 2007-03-05 10:00:53 2498.2973 2498.2973   FALSE   FALSE
2 F07001 1481274 6619628 2007-03-05 12:00:41  657.1029  657.1029    FALSE   FALSE
3 F07001 1481279 6619630 2007-03-05 14:01:12  660.3569  660.3569    FALSE   FALSE
4 F07001 1481271 6619700 2007-03-05 16:00:39  620.1397  620.1397    FALSE   FALSE

  in ArcGIS now looks like this:

Field1idid_Xid_YxydateR1dmedR1dmean R1errorR2errorOBJECTID *
1F07001118.0818119.485541e+01514824456621768NA2498.297272498.29727FALSEFALSE1
2F07001118.0818119.485541e+01514812746619628NA657.102922657.102922FALSEFALSE2
3F07001118.0818119.485541e+01514812796619630NA660.356911660.356911FALSEFALSE3
4F07001118.0818119.485541e+01514812716619700NA620.139702620.139702FALSEFALSE4
5F07001118.0818119.485541e+01514808496620321NA378.186792378.186792FALSEFALSE5

Where did id_X and id_Y come from?? What are they??
What happened to the Date column???  Why does the date column show up when I use write.csv but not write.table?

Thank you for your help.

~K
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